INTnODUCTION

( 1 )

Barreawil1 for the first time observed while

searching for a delicate test for the deteotion of

hydrogen pero:dae or dichromate present in tra.oeF.I, the

formation of a blue coloured substance by the interaction

of hydrogen peroxide and an acidified dichromate solution.

Barreawil (loa. cit.), ~oiasan2 , Conict', Riesenfeld4

and Wiede5 suggested various formula3 for this blue

substance and called it blue peroxychromic acid or simply blue

perchromic acid heoause of ita aci1ic nature observed bJ

them. Rejecting the acidic nature of the blue substance ,.

Schwarz and Giese0 called it a pentoxicle of chromium

and assigned the formula cr05 for it. Ver.y recently this

formula has again been contradicted by Rai et. al.7• 8 who

called it blue perchromate and assigned the fo~~la

Barreswil (loa. cit.) found this blue substance

to be unstable in the aqueous solution. It was found to be

more stable in the ethereaJ. solv.tion. Apart from the ether

solvent, Grigsi9 ann Grosvenor10 found that there were also

other oxygen oonta;.ning organic slllvents in which the blue

substance could be extracted trom the aqueous layer. These

solvents were eteyl acetate and valerate; amyl valerate,

butyrate, acetate, formate and chloridea and substituted

amyl alcohol. Among these solvents when the blue substance

was present in solution, 1 t was ordinarilJ found stable onlJ

for 1·2 hours at 0°C 1 exceptin~ ethyl acetate in which it

was shown to be most stable, i.e. approzimatelJ tor 2) hour8.

( 2 )

Grosvenor (loo. cit.) also obserTed that besidea

these oxygen containing organic solvents, other organic

solvents such as carbondisulfide, benzene, petroleum,

terpentine oil, castor oil, bergamot oil, oil of winter green,

paraffins, chloroform, carbon tetrachloride, toluene,

nitrobenzene and aniline did not dissolve the blue substance.

Here it will not be out of place to mention the name of

tributyl phosphate which has been used recently as an organic

solvent for the blue substance by Sastri and Sunder11 , and

Tuck and Watera12 •

This blue substance has eo far been known to be

present in the state of solution. Many investigators tried to

isolate it in the solid state but all their attempts failed.

They noted that on the evaporation of ethereal solution of

the b~~Q substance, the decomposition of blue substance

started with a hissing sound after a particular concentration13.

Apart from the reaction between hydrogen peroxide and

an acidified dichromate solution, other reactions were also

tried for the preparation of the blue substance, but they

failed. Further, since these other reactions are not of much

significant use, only one of them is being mentioned here.

When chromyl chloride was made to react with hydrogen peroxide,

it gave an equilibrium mixture which retained some of the

chromyl chloride and from this equilibrium mixture no definite

compound could be isolated14.

( 3 )

Here ~O.Cr(O)(o2 ) 2 has been assumed by Schwarz et.al. (loo.cit.)

as the species responsible for the blue colour present in

the aqueous or ethereal solution. Thus the Chemistry of the

blue substance is known only in the solution state.

It had long been noted that the presence of acid

was necessary during the reaction of hydrogen peroxide with

the dichromate or chromate solution to produce the blue

substance. Berthelot15 observed that the presence of strong

acids such as H2so4 and HCl, during the reaction of H202 with

dichromate produced blue colour whereas the presence of weak

acids such as acetic acid, phosphoric acid etc., the reaction

of r~02 with dichromate produced violet colour. Moreover the

colour of the resultant products changed even to brownish, if

more weak acids such as boric and hydrocyanic acids were

present during the reaction of hydrogen peroxide with

dichromate. He also observed that with the moderate

concentration of chromic acid, hydrogen peroxide produced

blue colour, but with the fall in the concentration of chromic

acid the colour produced by hydrogen peroxide changed from

blue to violet, brown or even to green. Thus with dilute

chromic acid solutions and at temperatures around 10°C, the

action of hydrogen peroxide produced blue colour, but it was

in traces and usually a brown colour predominated.

An interesting phenomenon of the inhibiting action

of certain substances had been noted by some investigatora

during the preparation of the blue substance. Werther1T

( 4 )

observed that the presence of small amounts of vanadate•

diminished the colour of the blue substance and this dimunition

depended on the concentration of the vanadates. It was

further shown by Richar417 that this inhibiting action of

vanadates could be counterbalanced by the addition of

small amounts of sodium hydrophosphate or hydroarsenate.

Besides vanadates, there were other compounds known for this

inhibiting action, vis. tungstates, molybdates, phosphates,

and arsenates. But the inhibiting action of these

substances was lese pronounced as compa~ed to the action of

vanadate a.

As regards the chemical action of the blue

substance, it had been found by Asohoff 18 that the ferrous

salts decolorized the blue colour of the ethereal solution.

Furthermore he found that on adding a dilute solution of

potassium hydroxide to the blue solution until the ethereal

layer assumed a pale-blue colour, the aqueous layer became

brownish-violet and on the addition of alkali solution in

excess, oxygen was evo~ved with the formation of alkali ' ' 19 chromate. This phenom~non had been confirmed by Sohonbein

and Iilartinon20 who also observed the immediate decomposition

of the blue colour of the ethereal solution with the formation

of alkali chromate, by the addition of aqueous alkali

siution. Mineral acids had also been shown to decolorise

the blue colour of the ethereaJ solution with the formation

of chromic salts. The organic acids, e.g. oxalic acid21 ,

had been shown to decompose the blue aubataaae.

( 5 )

It is thus found with the lapse of time that more

and more investigation& were performed to auggest the

appropriate formula tor the blue substance and in this way

the results of the investigation& were then interpreted by

various workers to justify their proposed structures and

formulae. This type of trend adopted by various investi~aters

although led to a better understanding of the structure of

the blue substance, but a final conception of the structure

could not be arrived at, because this needed the interpretation

of the results of investigations with an open mind. With

this view all the literature available on the subject has

been classified as follows:

1. Studies on the decomposition of hydrogen peroxide

catalyzed by aqueous chromic acid solution or by

aqueous/acidified dichromate solution.

2. Studies on the compounds derived from the ethereal

blue substance by nitrogenous organic bases or with

other basic substances.

3. Studies on the compounds formed by the reaction of

ethereal blue substance with alkeli and other alkaline

earth metals.

4. Studies on the decomposition products ot the

ethereal blue substance obtained under different

conditions.

5. Physico-che~cal studies of the ethereal blue

( 6 )

substance by potentiometric, conductometric,

molecular weight, magnetic, ultraviolet, intra red,

x-ray crystallographic and other spectroscopic

measurements.

(1) STUDIES ON THE CATALYTIC DECOMPOSITION OF HYDROGEN

PEROXIDE 1

One of the earlier methode adopted for the elucidation

of the structure of the blue perchromate, was to study the

catalytic decomposition of hydrogen peroxide and this

decomposition was carried out in the presence of either

chromic acid or dichromate or chromate solutions.'

It was Berthelot22 who for the f:i.rst time studied

the decomposition of hydrogen peroxide in the presence of

aqueous potassium dichromate solution. He observed that

with the addition of potassium dichromate solution to the

hydrogen peroxide, oxygen gas evolved qt.t.ite briskly and

the solution became deep brown in colour. Although he found

that colour was produced due to the formation of chromium -

chromate, but he could not prove the reduction of a part

of dichromate to produce Cr(III) to form chromium chromate.

He further observed that along with a deep brown colour, a

trace of blue colour also appeared. These colours existed

only for a short time and finally the colour of the solution

tln'Iled to that of the dichromate solution. He, therefore,

concluded that a small amount of dichromate solution could

decompose an enormous quantity of hydrogen peroxide and

that too without itself being affected.

( 7 )

Baoh23 studied the decomposition of hydrogen

peroxide in presence of chromic acid. He observed that

during the reaction an intermediate brown coloured adduct

was formed, which decomposed spontaneouslJ with the

liberation of oxygen and with the regeneration of chromic

acid. Thus in this case alae the total quantity of hJdrogen

peroxide waa decomposed without affecting the catalyst,

i.e. chromic acid. Bach (loc. cit.) had further shown that

the mode of decomposition changed with the presence of

sulphuric acid, and he represented the reaction by the

equation.

In this reaction he had shown that chromic acid and

h1drogen peroxide reacted in the molar ratio of 1 a !, to

liberate all the active oxrgen ot the hydrogen peroxide and,

that the catalyst chromic acid was ~educed to Cr(III).

Spitals~4 also worked in the same direction and

he carried further the work of Bach. He attempted to

measure the velocity of the decomposition of hydrogen

peroxide by using the catalyst, chromic acid and found

that due to the presence of the excess of hydrogen peroxide

about 28% of chromic acid had been reduced to Cr(III). The

reduction of chromic acid was found to be independent of

the initial concentrations of either hydrogen peroxide or

chromic acid solutions. Spitalek725 also studied the

catalytic decomposition of hydrogen peroxide b7 the acidified

( 8 )

potassium dichromate solution and even in this case also

about 28% of dichromate was found to be reduced to Cr(III).

Thus the same constant ratio between Cr(III) ot

the reduced dichromate and the Cr(VI) of the remaining

dichromate had been maintained by both the investigators,

Bach and Spitalsky (loc. cit.) in the reaction between ~02 and dichromate, nnd they found that the amount of re'uction

of d.ichrorr.ate did not depend on the concentrations of the

reactants provided the amount of ~02 was in excess.

Further improvement in the understanding of the

reaction between hydrogen peroxide and chromic acid was

made by Riesenfeld26 • He agreed with epitalsky's views

(loc. cit.) that there remained. a constant ratio between

the hexavalent chromium (of unred.uced chromic acid) and the

trivalent chromium (of chromic salts obtained from the

reduction of chromic acid) after the completion of the

reaction between chromic acid and hydrogen peroxide. He

supnorted his statement by giving the followi~g equation

and mailltained that the hydrogen peroxide lllURt be in excess

as compared to the quantity of c~romic acid.

In this reaction he had shown quite clearly that

chromic acid did not act merely as a catP.lyst but actually

took part in the reaction. Thus the hydrogen pe~oxide had

reduced the eame fixed proportion of chromic acid in the

( 9 )

presence of hydrogen ions to form chromium dichromate. He

explained that during the reaction bet-.en hydrogen peroxide

and chromic acid, a blue substance was formed which existed

!or a short while and then decomposed to produce chromium -

dichromate, c~2 (cr2o7 )3 , with the liberation of all the

oxygen.

Riesenfela27 and SpitalakJ29 observed that the

aqueous solution of chromate and dichromate also decomposed

~02 catalytically. In oontinuation with this work 11obertson29

observed that the decomposition of hydrogen peroxide by a

mixture of chromate and dichromate was promoted bynanganese

salts. Rubinshetin)O also found the effect of cadmium sulphate

in the same conditions.

Riesenfeld, Kutsch and Ohi31 studied the decomposition

of hydrogen peroxide by an aqueous solation of potassium

dichromate acidi£ied with sulphuric acid and observed the

appearance of a blue colour which being unstable decomposed

to liberate oxygen. They estimated the liberated oxygen

and found that the amount of oxygen fOJ'Illed we.s always less

than the theoretically calculated val~e. They further

suggested that the blue compound was a mixture of H3cre8 ,

H3r.ra

7 and an anhydride CrO 4 •

Bancroft and ~2 studied the catalytic

decomposition of hydrogen peroxide by the method of e.m.f.

measurements and pointed out t~at the oxidation state of

chromium in the blue compound is not higher than +6 state.

( 10 )

RumtlJ etu41e4 the oatalrtla 4eoo•poe1t1on ot

hyt'-ro~en perox14tt b7 the ao141t'hd ol'n·o-te or 41fth!'Milte

solution" und extracted the bl .. coMpound bf t~e or~~ia solvente. Depondina on the Job'e oont1nuoue veriotloa

metho1, he aenir,ned the ro~la ft2Cr06 to the bluft compound.

;l'in"llY to 1um:nnriee the ltud1e' made on the oatalytia

decom-,o'l1.t1.on o., !lydror:en pe.,..orldo b7 o't'I'Omio acid o.,.

e.cU:t 1'1cd :-1P•omn to I :Uohromuta solutions, it oan be enid

thut the rAduotion of ohromic e.oic! or ohro:llllte I dic'h"T"O:natl

roquirea hydro:~en ionea and th11t the blue 1ubatanoe e.ppear1

only in the abo·ce conditions of' the reaction. Therefore,

it ma.y ba concludad thr.t the hydrogan ions mu11t heve eome

definite role in the formation of the blue substance and

also that the process of' reduction of hexavalent to trivalant

chromium muat be some how connected with the mechanism of

the for@ation of blue substance.

(2) STUDIES ON THE COMPOUNDS DERIVED FROM THE ETHEREAL

BLUE SUBSTANCE.

The studies made on the compounds obtained by the

indirect or the direct action of the ethereal blue substance

are being classified in to three categories :

(A) Studies of the compounds obtained by the interaction

of ethereal blue substance with organic nitrogenous

bases.

This category has again been subdivided in to two

classes :

( ,, )

(i) Studies of the oompounde obtnined b,r the dire~t

1nteruot1on ot t! .• ethereal blve subetnnoe w1 <;b the

organio uitrogeuoua bases.

(11) ntudj ee or tlte compounds obtuinod by the inclireot

intet•(lo tion of the otthereal blue rJubetnnoo w1 th the

organic nitrogenous basel.

(B) Stuclillf! >~ tha r,;ol9jJOt.mda obtaine l by t~e interaction

of ~t:wr..1o.l bluo aubstt-•190 •:t1th al!calies or the salts

o! ulkali•Js,

This oa tegory hna ulso been sub divided in to two

cle.s·Jes.

(i) The red tetra peroYyohromates and thei~ derivatives.

(ii) The violet di peroxyohromates and their derivatives,

(C) Stud.ies of the common derivative of ethereal bh•.e

subste.nce s.nd thr: substanc- ee coming tmder oatee;ory

'L' and 'B'.

(A) (i), Wiede34 • 35 treated the ethereal solution of the

blue substance with pyridine and anilJne. After evapol•ating

ether from th.e reaction mixture, he obtained solid compounds

and assienad the formula. Py .Rcr05

and An.HCr05

for the

compounds obtained from pyridine and aniline respectively.

Here Py means pyridine and An means aniline.

In these studies Wiede (loo. cit.) regarded the

blue substance to be an acid, having the torrnula IiCro5 and

called it blue pe:rchromic acid. Thus the solids obtained by

( 12 )

the int(lraction of the so called blue perchromic acid

Considering the acidic nature of the blue substance

more solid compounds were prepared by the interaction of

quinoline35, 1.10 - phenanthroline36, dipyridyl37 and

strychnine38 • These solid compounds were, however, regarded

as adducts 1 w:lils th2 solid >JC11:pound3 obtained by t 11e

am:rrorcb.:n hydroxi'.~·.~, trimathyl amine and piperidine were

regarded as saltsJ5.

Out of these salts I adducts, Schwarz and Giese6

studied the reactions of pyridine derivative, and on the

basis of its 1•eactio·1a with dilute sulphuric acid, with

sil'Ter (I) oxld~, a:1.i neutral potasSium permfl.nganate (o-f which

8 H+ + 2 Py. Cr(0)(02 )2

Py.Cr(0)(02 )2 + A~O

= ..

cr+J + 3 H2o+ 7/2 o2/ 2 Pylt.

A~cre4 + Py + 02 •

four equivalents were consumed per mole of pyridine complex ),

they aug~ested the composition of tha pyridine derivative

as :Py.Cr(0)(02 )2 and the composition of ethereal blue

substance as Or( 0) ( o2 )2 • So ao.::ording to Schwarz and Giese

(loc. cit.) these salte/adJucts were knc.wn to have the general

for:aula :3.Cr05 , where :3 stood for tlie org"l.nic nitrogenous

base.

In the pr,,se:lt 11 ter~.ture of the derintives of

tr est- orgcnic ni troge:.ous bases, a different interpretation

is >:lao found a!:lout t':e strt.:cttires of these de-ivativea.

( 13 )

Ra139, an<l Pilla:!. nn (l Ra140 propo::1ed thn t tha so lid

cor-1poundn fo:':'mc•i ch1n to the i:J';rn•action of. atheroal blt~e

substance 1rTi th p~r:;.•idina, piperidine. quinollne. e-hyilroxy

quino1ino, atrJchnine and hexa methyle:-~e tetramine \Vere not

ad.du~tn but th<ly werG complexes havtne Cohromiua (III)-baa.D'

cation. Thus they regarded the blue substance to be

chromium (III) perohromate having the formula Cr~II(Cr~Io10 > 3 •

drJr:i.vr.ti •1e hed belln shown +.o eX!Jlode if it \Vas either heated

to 70°C, or treated with concentrated sulpburic aoid41 •

The deri vati veFcJ of the b:i.dentate ligands had 'tie en found to

be more stable thermally as compared to those of monodentate

lignnds36 • 37 •

(A) (ii) Hcfmann42 pr?p:>.red th.e deT.':i.vati ves o.f' ethylene

diamine aud hexamethyl~ne tetramine bases by treating a

mixture of corresponding amines and chromic acid with '0%

hydrogen pe~oxide at o0c. He assigned the formula

c2H8N2• Cr(02 ) 2• 2H2o for the ethylene diamine derivative

and the forr~le c6H12N4• Cr(o2) 2 for the hexamethylene

tetra~llne derivative, but he did not determine t~e structures

of these compounds.

(B) (i) Rieser.feld, Kuts~h a~d ~ohlera43 obse~ve1 that by

the action of hydrogen peroxide on an alkaline solution ot

an alkali chroill.~te at o0 c, dark brown crystals se~nrat~d

slowly fro:r; the cold solution. In this way they prenP-red

the codiur.., potassium :nd G.m:r,onium sal +.s of the red

( 14 )

tatraperozy chroma-tea by the oxidation of the eolu'.;ions

of oorre~)OU.•llng c.lkali ohromatee. H.iesenfeld4t, 44 also

studied t:1e decompoaitlon of these compounds by the action

of ad<l:l.c, al:caline and neutral potassium permanganate

solGt~.ons. He estiruated the liberated oxygen and found

the.t four peroxy groups per mole ware pree0~t. Thus on

the basis of the anF~lysis a general formula• f'I •J Cr(02 ) 4 was proposed for the red tetreperoxy ohromr.teo. Het'e :!.~

means the monovalent alkali metal. These s~lt~ were,

however, supposed to be the derivatives of a hypothetic

acid II3cr08 •

RieRenfeld and coworkera45 observed t:1at a red

or a reddish-brown salt, triammonium tetra peroxy chromate

(NH4

)3

Cr(02 )4 , was formed by the action of an excess

of hydrogen peroxide on the weakly ammonical solutions,

otherwise, if, these conditions were not strictly adhered

to, triam.aino diperoxy chromium (IV), Cr(02 ) 2 .3NH3 was

obtained.

As regards the tnermal stability of the salta of

tetraperoxy chromates, F~esenfeld and coworkers43 found that"

po:.">s:.litLil s:';.ltB were more stable than ammonium and sodium

salts. These s;;.lts had been found to be sli~htly soluble

in W<-",ter, a:1d their mode of decomposition in aqueous solution

depend~d on the pH of the solution. In elkaline or neutral

medium the s2lts yielded. oxy':'"er, 3.!1d c!-.romete, whe:r.-eae in

acidic solution tJ,'ly yielde;i cl;rcmium (III). These s::lts

had f11rther been shown to b'l con- e.,.ted by t~e treat::1ent of

( 15 )

acid at low temperature in to the blue substance which

could be extracted in to the ethereal layer.

Riesenfe lil •md Mau46 had shown that t11e amoul"'.t ot

bl1.1e substance formed, de-pended on the etre'1gth of the

acids. They had also shown that the red potas9ium or

scdi~~ tetraperoxy chromates could be decomposed by means

of any acid to form the blue substance, only in presence

of water. Otherwise anhydrous acids decomposed red salts

to chromatea. rhes, therefore, concluded that red tetraperoxy

chro~~tes must be considered as anhydrous salts of the blue

substance w]lich they called blue perohrornio aoid. They 0~

suggeated the constitution of :!'!!d SA.lts as 0~ Cr(O.OM) 3 and the oon~titution of the oorresnonding acid as

(OH) 4.cr(O.OH) 3 or simply as, H3c:r.o8 .2H2o • He'!:'e the wah!'

molecules shomt in th.e formula of blue substance were

considert=t<'l as water of crystallization because the blue coloul'

resulted only when water was present during the interaction

of red tetra per.oxy chromate (V) with the anhydrous acid.

(B) (ii) Riesenfeld, Kutsch Run Wohler.s43 rm~c;ested a

gener"ll met~o1 fo'J' the pre')ara+.ion of th<'! •r:l.ob"; salts by

the P.Ction of hydrogen pel'O'ltidP. on we"\kJ.y aci'lic soJ:utio"1.s

or "!letal cnromRtes. 'l'hsy pro,,ose" "';h('! f'orrrlula, KH2~r07 and

( NH4). ~cr07 foY.' the viol"!t s>l.l t.R of ':"l"t:lssittn and alltTonium.

Thus they reg~rded the violet salts to be the derivati•ree

of a hypothetic ncii, H3cr07 •

of violet sro.lts. He prepared t"le violet s·"lts of am~or:ium

end potassium res~ectively by reacting t~e et1ereal blue

( 16 )

substance with lese than the calculated quantity of

ethereal ammonia and w1 th alc.oholio potassium hy-droxide

or aqueous potassium oY,hide solutions.

The unstable nature of these violet aalts created

difficulties in aetermining their compositions and for a

long time they were believed to have the general composition

Micr06 .~o as proposed by Sohwars and Giesa48 •

Grif'f'ith49 treated these violet salts with potassium

permangemate, eerie sulphate or silver (I) oxide and

showed that two peroxy groupe to each chromium atom were

present. He also studied these salts by different physico -

chemical methods and established their composition,

mi[CrVI(o){o2 )2oH] • The aqueous solutions of the violet

salts were neutral to litmus and their aqueous solutions

had low conductivity which suggested that the proton

present in the anion was not mobile. The violet salts

were extremely unstable and exploded when struck or warmed.

They decomposed in water or even in the solid state to

give oxygen and chromic acid or chromate.

(C) It bad been shown by the earlier investigators

that the ethereal blue substance, red tetra peroXY"chromates

and violet diperoxychromates were inter related structurally

with eGch other, because they could easily be inter

converted and also, because a common derivative, tria~~ino

diperoxychromium could be prep8red from each of them.

( 17 )

Riesenfeld, Wohlers and Kutsch43 had already

demonstrated that the alkaline solutions of metal chromates

yielded red tetra peroxychromates on treatment with

hydrogen peroxide while the weakly acidic solutions of

the metal chromates yielded violet diperoxychromates on

treatment with hydrogen peroxide. Similarly Barreswil

(loc. cit.) had shown quite early that by treating hydrogen

peroxide with a cold and moderately acidified solution

of chromate yielded blue substance which was extrated

by ether.

The ether extracted blue substance had also been

sho·~ to be prepared by Riesenfeld and Mau5° after

acidifying the red tetra peroxychromates at low temperatures,

and it was also shown to be prepared by Hofmann and

Hiendlmaier51 after acidifYing the cold aqueous solutions

of violet diperoxychromates.

Riesenfeld, Kutsch, Ohl and Wohlers52 converted

red salts in to violet salts. They took an aqueous paste

of red ammonium tetra peroxychromate and after acidifYing

it, they found that violet ammonium tetra peroxychromate

was precipitated, whereas the action of alkali on violet

salts led to the formation of red tetra peroxychromates.

Riesenfeld, Wohlers R~d K~tsch4 3 had shown that

a common derivative which was a b:ro•.m red coloured

crystalline solid of t'1e composition Cr{ o2) 2• Jirn3

,

was prepared f~om ~ny of these com~ounds (a) red tetra

( 18 )

peroxychromate. (b) violet diperoxychromate and

(c) ethereal blue substance, by the action of an excess

of amnonia. The same compound had also been shown to

be formed by Hofmann and Hiendlmaier53 due to the reaction

of ammonium dichromate, aqueous ammonia and hydrogen

peroxide.

Riesenfeld41 showed that triammino diperoxy

chromium was a rebtivel;y stable compound and exploded

if grounded up or heated. This compound decomposed to

give hexamine chromium-(III)-ohromate and was found to

dissolve in water and produce a red violet colour. This

solution after the treatment vdth an acid produced the blue

substance which was then extracted by ether34, 53 •

The compound tria.mr:dno diperoxy chromium54 was

found to react with potassium cyanide solution at 60°C

to produce cre4.3 KCN. Riesenfeld a!ld Weseh55 determined

the molecular weight by the cryoscopic method and assigned

the structure of triammino diperoxyohromium as,

H)N~ _.-----0

H)N Cr 0

HN~ ~0 3 2

and in sup~ort of this formula, the dicyano monoamine

derivative which was inter mediate between the trioyano

compound, cro4 .3 K0N and triammino oonpound, cro4.( NH3

)3

,

qs prepured. The structure of the trioyano derivative

of triam;nino diperoxychromium is given as,

( 19 )

cw----__ o CN Cr------ 0

CN~ -------02

Thus on the basis of studies made on the products

formed by the interaction of ethereal blue substance with

organic nitrogenous bases and alkalies, it may be co~cluded

thrrt the various formulas sug~ested for t~e ethereal blue

substll.nce are : IICro5 , cro5 , H3cra8 , ~cro6 or cra5.~o , and cr2 (cr2o10)

3 •

( 3) STUDIEfL.9N ~JiL.@MPOUNDS FORMED BY THE RF..ACTION

OF ETEEREAL BLUE SUBS~\NCE WITH ALKUI AND OTHER

AI,KALINE EARTH mETA!&•

Haussermann56 observed that by the reaction of

an aqueous suspension of Cr(OI-I) 3 and hydrogen peroxide

at 10° - 12°c, reddish bro~Ti crystals separated. He

assigned the fcr:uula Na6 cr2 o15• 28 H2 0 to this compound.

He decom:co3ed these crystals by dilute sul9huric acid

but could not observe the formation of an intermediate

blue compound.

Horace, Byers and Reid57 noted that IJlatals evolved

hydrogen gas when treated with the et~ereal blue substance,

and thus showed the aci:lic nature of t;le blue substance.

They used t'c.e mete.ls notassiur::~, sodium, lithium, ma~esium,

calcium, barium And zinc. In case of the compound formed

by the FiCtion of ootassium on the st:1ereel blue substance,

they found the compound had the composition Kcr04 or ~cr2o8

( 20 )

and the compounds formed by different metals in the

same way had the composition ~cr2o8 (M means monovalent

metals). They, therefore, oame to the conclusion that

the ethereal blue substance must be having the composition,

~cr2o8 and this composition depended on. the concentration

of hydrogen peroxide used for the preparation of the

ethereal blue substance,otherwise the higher concentrations

of hydrogen peroxicle would have yielded t~e hi~hly oxidized

compounds of the metals.

Raynolds and Reedy58 observed that the aqueous

alkaline suspension of chromic hydroxide produced a red

coloured solution by the treatment of 30% hydrogen peroxide.

They found that the red coloured calcium perohromate

prepared by a similar method had the composition,

ca3cr2o12 .12 ~0 which exploded on raising the temperature

to 100°C. The aqueous red coloured suspension of calcium

perchromate changed to blue colour (extractable in ether)

on its treatment with dilute acids. In the red calcium

perchromate, Cr (III) had been suggested to be attached

with the peroxy groups but Martinez and Porter59 disagreed

with this suggestion and proposed another structure,

./" 0 - 0"'-Ca 'Cr=O ~o-o'i ____..-0-0

Ca ~0-0"'­./"0--0-Cr=O

Ca~ / 0-0

.10 ~0

i'his struct re h~d bee!l su-,,o~·te1 on t~e basi~ of ita

( 21 )

resemblance with Na6cr2o15 .1o ~0 because the same

red coloured calcium perchromate was precipitated by

the action of calci~~ chloride solution on sodium

perohromate.

Rosenheim, Hakki and Krause60 treated sodium

and potassiu::J ohromates with )0% hydrogen peroxide at

0°c and obtained the corresponding perchromates having

the oom,osition, Na6cr2o15.n ~0 and K6cr2o16.n ~0 •

But the lithium perchromate prepared by the same procedure

had two different compositions, Li6cr2o13 and Li6Cr2o15 under slightly changed conditions.

Martines, Rodrigenea and Brito61 also prepared

red perchromates of magnesium by treating a solution of

magnesium nitrate in 30% H202 with sodium and potassium

chromates at -1o0c. These solids had the compositions,

Martines and Ade1162 • 63 reacted an aqueous

solution nf magnesium chromate and magnesium oxide with

30% hydrogen pe~oxide at -5°0, and obtained dark red

coloured crystals which were fairly soluble in water.

The composition of the compound was Mg3cr2o16 .26 ~0 •

Other compou_~d havin~ the composition, ca3cr2o16 .15 E20 was prepared by treqting calcium c':loride solution with

a well cooleu S:l.~urated solution of ~cr2o 16 • In alkaline

solution the douJle salts of these perchromates were prepared.

( 22 )

By the reaotion of calcium chromate and 55%

hydrogen peroxide in the presence of ethyl alcohol,

Bogdanov, Petrova and Minaev64 obtained dark brown

crystals of cacr06.n ~0 •

It had also been suggested65 on the basis of

oxygen exchange studies, that a peroxy cation of chromium

might be forr;led as an intermediate product due to the

action of peroxide on solutions of Cr (II).

In connection with these studies a peculiar

phenomenon had been observed by Fujioka and Cady66 that

a blue green so called perchromic acid was formed by the

reaction of chromic acid with hydrogen peroxide in

presence of trifluoro acetic acid.

(4) STUDIES ON DECOmPOSITION PRODUCTS OF ETHEREAL

BLUE SUBSTANCE.

So far we have seen that the catalytic decomposition

of hydrogen peroxide by the aqueous solutions of chromic

acid and acidified dichromate or chromate had been studied

and the various investigators tried to elucidate the

mechanism for the formation of the ethereal blue substance.

Apart from this the reactions between the ethereal blue

substance and organic nitrogenous bases or alkali of

few metals, had been studied in search of the comnosition

of t~e ethereal blue compound. In a similar way the

decomposition of ethereal blue substance and the identi­

fication of its decomposition products had been utilized to

( 23 )

determine the composition ot the blue substance.

Moiasan67 was the first person who tried to

isolate the blue substance trom the ethereal solution

by evaporating the ether solvent very carefully at -2o0 c,

but he could obtain a blue oily liquid which was very

much unstable and decomposed to yield chromic acid. Rai68

also tried to isolate the blue substance from the ethereal

solution by slowly evaporating the ether solvent with the

help of a vacuum pump. He observe1 that after a particular

concentration the ethereal blue substance decomposed with

a hissing sound and produced chromium dichromate.

Schwarz and Elstner69 prepared the blue substance

by treating chromic acid with hydrogen peroxide and

extracted this blue substance in dimethyl ether. From

this dimethyl ether they tried to isolate the blue substance

by evaporPting the ether at -50°C and obtained blue crystals

of the ethereate. Riesenfeld and Mau 70 fou."l.d these crystals

to exulode l'lhen warmed up to -J0°C and they thought these

crystals to be H3cr(o2)4 • This composition of the crystals

was corrected by Schwarz and Elstner (loc. cit.), and they

presented them as Me2o.cr05 • Therefore they regarde1 the

ethereal blue substance as cr05 • Wi t'1 this idea Bobtelsky

et.al.71 sug~ested that the blue substance present in

the aqueous solution could be regarded a hydrated pentoxide,

H20.cr05 or H2Cr06 , and to account for the reactions of

the blue substance in aqueous solutions, Aschoff18 had

( 24 )

earlier suggested the following equilibrium to exist.

Bobtelsky et. al. (loc. oit.) observed that the

aqueous solution uf the blue substance decomposed rapidly

to give oxygen and compounds having Cr (III) at pH less

than 4, where-as the amount of Cr (VI) in the solution of

decom~oeition product increased with the increase of pH of

the solution.

Rai and Prakaeh7J, 74 had shown the decomposition

of ethereal blue substance in water to produce chromium

dichromate, (Jr2(cr2o7) 3 and concluded the composition of

the ethereal blue substance, cr2(cr2o10) 3 • They had also

shown the changed behaviour of the ethereal blue substance

in presec1ce of an ex'lees of hydrogen peroxide due to the

followin~ equilibriam.

Pillai ana Rai75 P-xtracted the blue substance

from the aqueous reaction mixture by ethy:!. acetate i:2stead

of ether and found that it decomposed in water to produce,

cr2 (cr2o8 )3 instead of Cr2 (cr2o7)3 • Thus the formation

of this compound had been attributerl to the greater

stability of the blue substance in ethyl acetate solution

instead of the ether solution. Singh and Rai76 improved

u~on their work and enid that t~e compoeition of t~c aqueous

decomposition product of the blue substance 111 not chan~e

( 25 )

merely by ohangine the solvents which were used for

extracting the blue substance imnediately after its

preparation, but the aqueous ••composition products were

always found to be a mixture of Cr2(cr2o7) 3 and cr2(cr2o8)3 •

Here ethyl acetate or ether in whose solution the blue

substance was present, did not have any effect on the

mode c.-· decompositt0n of blue substance in water. They

therefore, su.g·;ested that the decompos:i.tion of ethereal

blue substance in large volume of water produced

Cr2(cr2o7)3 , and if it was decomposed in a buffer solution

of pH 5.50- 6.86 another compound, cr2(cr2o8)3 was obtained.

Rai and Rajput77 prepared the water decomposition

product of the ethereal blue substance in a large volume

of water and separated Or (III) and Cr (VI) by the ion -

exchanr;e method. On estimation Cr (III) and Cr (VI) ions

were fow1d to be present in the ratio of 1 1 3 in the water

decol'lposi tion product and on this basis tlley suggested

the formulc. Cr2(cr2o7) 3 for the water decomposition product.

The identification of another compound chromium

peroxydiohromate, Cr2 (cr2o8)~ had been done by physico -

cher-Ji~al s.nd J.-.inetic studiee~ 76, 78, 79, 80, 81 •.

Rajput82 prepared the ether extracted blue

substance by the ref-ctio-- of potassiun dichromate, tartaric

acid r.nd hydrogen ;>eroxide. lie found that t!-)~ water

decomposition product of etheraal blue aub~t~nce was

(CrT) 2cr2o7 , and this was quite in agreene~t with the

( 26 )

SU/~I',ested compoei t:l.on, Or2 (or2o7)) of the water d.eco:npoai tion

product (loc. cit.) in which Or (III) was aimilar11

present along with Or (VI). This latter ethereal blue

substance was prepared by the reaetion of' dichromate,

sulphuric acid .~nd hydrogen pe.,..oxide.

Different blue substances of different compositions

had a::!.so been prepared by t~le reE:otions

poto.ssium diclp·oma te ar~d various acids.

of hyclro,~elJ pE'l:roxide,

Singh8), Rai 84

ttnd Awasthi05 used phthalic, hydrofluoric and adipic

acids respectively to acidify the ll2Cr2o7 solution in the

prepar~tion of different ethereal blue substances having

the com:Jositions, (Cr phth) 3 [cr(cr2o10) 3 J , (OrF2)2 .cr2o10 and (Cr Ad)

3 [Cr(cr

2o10) 3] respectively. They found that

these ethere3l blue substances decomposed in water to

p~oduce, (Cr pb:ch) 3 [cr(cr2o6)3] , (CrF2 )2 .cr2o7 and

(Cr Ad)) [Gr(C:•2v7)3] respectiYely.

Fur"cher ethereal blue aubA'.;ance p1•epr.re1 by

sulphuric ecid was also decomposed by keeping in open

and in closed bottle conditio~s. Rajnut82 fou~d that in

open bottle condition the decomposition p!'oduct obt.ained

was chro~ium c~!'om~te cr2 (cro4 )~ and in tha elosed bottle

clo~ed bot~le condition the decomposition product obtained

was chromous chro~te, Cr(Cr04) ; while t~e decomposition

----------------------------------------------------------T • tartcrate ion, phth Q phthalate ion, F = Fluoride ion

Ad • adipate ion •

( 27 )

products of the ethereal blue substance prepared with

phthalic, hydrofluoric and adipic aoide in the open bottle

condition were,[mixture ot (Cr phth) 20 & crcr04],

(CrF2)2 • Cr2o6 and (Cr Ad) 3 [cr(cr06>3l respectively,

whereas in the closed bottle condition they were mixtures

of (Cr Phth) 2o & Crcr04 , (CrF2)20 & CrCr2o7 and (Cr Ad) 20

& crcr04 respectively.

The composition, cr2(cr04)3 of the decomposition

product obtained in the open bottle condition from the

ethereal blue substance which was prepared with H2S04 ,

had been confirmed by Rajput and Rat66 by the ion exchange

studies.

Thus on the basis of the studies on decomposition

products obtained from the ethereal blue substance under

different conditions, the two compositions of the ethereal

blue substance are found worth consideration : (1) crV1o5

according to Schwarz and Giese (loc. cit.), in which only

Cr(VI) is present and (11) Cr~II(Cr~1o10 ) 3 • according to

Rai and others (loo. cit.), in which Cr(III) and Cr(VI),

both are present.

( 5) PHYSICO CHE~ICAL STUDIES OF THE BLUE SUBSTANCE.

'

These have been arranged under the following titles.

(A) Spectro-photometric studies :

(i) Absorption spectrophotometry,

(ii) Infra red spectrophotometry, and

(iii) Ultra violet spectrophoto~etry.

( 28 )

(B) Magnetic measuremen~•·

(C) X-ray orzstallograpbio meaeuremente.

(D) Conduotometrio measurements, and

(E) The determination of molecular weight!.

(A) Spectrophotometric atudiel t

(i) Absorptionspeotrophotometry t

r&ne. P. Rumpt87 supported the composition, cr05 of the blue substance by measuring the absorption of 1ight

at equal time intervals, of a solution containing ~02 and acidified H2Cr2o7 solution in the equimolar proportion

and whose pH value was maintained below 4. She observed

that the maximum concentration of the blue substance was

obtained when the ratio of the molar concentration of

~02 and acidified H2Cr2o7 solution was 1 : 0.5 •

Bobtelsky, Glasner and Bobtelsky - Chiakin88

confirmed the view of spitalsky and Kobsev (loo. cit.)

by the spectrophotometric and pH metric studies that the

two types of perchromio acids or simply perohromates where

formed in the reaction between chromic acid and Hydrogen

peroxide solutions. One, blue perchromic acid or simply

blue perchromate was formed at the pH value of 4 , and

another violet perohromic acid or simply violet perchromate

was formed beyond the pH value of 4 • These two forms

of the perchromic acid or simply perchromates were found

in equilibrium with each other and the tra~sformation of

one in to another was found not to involve hydrogen ions.

( 29 )

Glaaner89 confirmed the formation of the above

mentioned blue and violet substances and agreed with the

suggestion of Riesenfeld90 , that in the reaction one

molecule of' chromic acid reacted with one and halt

molecules of hydrogen peroxide to give one molecule of

the blue substance.

Glasner and Steinberg91 measured the optical

density of various solutions and found that hydrogen

peroxide reacted with chromic acid solution in the molar

ratio of 1.5 : 1 • That further found that, when X2Cr2o7 or N2Cr o4 solutions were acidified With strong acids,

hydrogen peroxide reacted with them in the molar ratio of

2 : 1 , while in case of K2Cr2o7 or H2Cr04 solutions

acidified with weak acids, hydrogen peroxide reacted with

them in the molar ratio of 4 : 1 •

(ii) Infra red spectrophotometry,

Evans92 recorded the infra red spectra of pyridine

and 1 : 10 phenanthroline complexes of the blue compound,

along with pyridine compouLds, Fy.HNO) and (Ag.Py}NO) in

nujol or hexaohlcro butadiene over a region of 2 - 15 !'- •

These soeotra of the organic base - blue compound complexes

were found similar to that of the pyridine complex, (Ag.Py)NO)

and they did not show any peak corresponding to N-H group,

which was normally exryected in case of the blue comnound

havin~ acidic nature. On the comnarision of the spectrum

of (Ag.Py)N0 3 with that of the correa~ondin~ pyridine-blue

( )0 )

compound, complex, it was found in case of both the

complexes that pyridine base hadeoordinated with the

metal ions in a similar manner.

Griffith93 studied the infra red spectrum of

the anhydrous potassium salt of violet dipe~oxy chromate,

and after identifying a peak corresponding to O·H

he formulatea the compound as K [ CrVI(O) (02)20H]

group,

• The potassium salt of the violet diperoxyohromate was

found to possessthe same number of peroxy groups per

chromium atom as the blue compound, Cr(0)(02)2 possessed

and, therefore, the blue compound was found to be easily

converted in to the violet salts by the mere addition

of hydroxyl ions.

(iii) Ultra violet spectrophotometry a

Fergusson, Wilkins and Young94 studied the

pyridine and 1:10 phenanthroline complexes of the blue

compound by this method and found that in the pyridine

derivative, the chromium atom present was in a sense six

coordinated, but the ligands formed a pentagonal pyramid,

so that there was what might be called a vacant coordination

position axial to the unique oxygen atom. In the ad~uct

of bidentate diamine, this position might well be fille1.

But they observed that the ultra violet spectrum of

1110 phenanthroline was rather different. They further

sug~eated th~t the infra red ba~da assigned to modes of

the peroxy groups in the spectra of the two compounds

( 31 )

in the NaCl region, howeve~, were at the similar

frequen~iea.

Shibata and 1~tsuno95 measured the ultra violet

spectrum of 3 NH3.cr(02)2 complex and contradicted the

formula su-;<?.;ested by Hofmann and Hiendlmair, and Riesen:f'eld,

Kutsch and Ohl (loc. cit) for the derivatives of diperoxy -

chromium and showea that the compound was polymorphic and

existed in two isomeri·~ forms.

(B) Magnetic Nieasuremeni!L:

Tjabbea96 found that the potassium red pero~romate,

K3

Cr(02)4 was paramagnatic and the value of its magnetic

susceptibility was 1.8 B.M. Analogous to this compound

Klemm and Werth97 obtained the value of magnetic

susceptibility of rel tetra peroxy chromate 1.8 B.M. ,

thus confirming the view that it contained pentavalent

chromi~~. They also studied the paramagnetic susceptibi­

lities of the blue a"ld violet di"?e::-oxyc:.romates and found

them to contain hexavalent chromium.

Bhatnagar, Prakash and Hamid9~ and Fergusson and

Wilkins (loc. cit.) measured the magnetic susceptibility

of Cr(02)2 .3 NH3 , a derivative of diperoxychromium 3nd

found it to have the value of 2 .a B.M. • The paralll8 gne tic

mor.;ent of this compoun:l. was consistent w1 th the -presence

of two unpaired electrons aasociate~ with c~ro~ium(IV).

Ra199 studied the parama.~etio properties of the

blue compound extracted by both ether and ethyl ac~tate.

( 32 )

Pillai100 measured the magnetic susceptibility

of quinoline and a-Hydroxy quinoline complexes of the

blue compound and found them to have the values of 3.80

and 3.88 B.M. respectively. He, therefore, SC~ggested the

presence of trivalent chromium in the quinoline and

8-Hydroxy quinoline complexes of the blue compound. He

also showed that the strychnine complex of the blue compound

had feeble paramagnetic properties.

Singh101 prepared the 8-hydroxy quinoline complex

of the blue compound which was prepared in turn either by

sulphuric acid or by phthalic acid and found them to have

the values of magnetic susceptibilities, 3.98 and 3.64 B.M.

respectively. Similarly the isoquinoline complexes of the

blue compound prepared either by sulphuric acid or by

phthalic acid, had the values of magnetic suceptibilities,

3.35 and 3.03 B.M. respectively. Thus on the basis of the

magnetic measurements Pillai (loc. cit.) and Singh (loc. cit.)

concluded that the ethereal blue compound formed complexes

with the organic nitrogenous bases and these complexes

had Cr in the trivalent state also.

(C) X-RAY Crystallographic Measurements :

X-ray study of a single crystal of the potassium

salt of tetraperoxyohromate (V), ~) Cr(02)4 was made by

Sternberg and Brosset102 • They found that the chromium

atom was surrounded by four equivalent peroxy grouns, in

an arrangement that could be described as a distorted

( 33 )

dodecahedron of oxygen atoms {figure given below) and

th0 t 11/0 Cr - 0 distances were significantly different.

Swalen and Ibera103 made the molecular orbital

calculatio~s using parameters derived from the g values

and assigned a B1 orbital of chromium to the unpaired

electron~ Abrahams and Kalnajs104 found the 0- 0

distance in the compound, of 1.40 A0 which was rather lees

than the value 1.49 A0 found in alkali metal peroxides,

perhaps because electrons that in the free pe~oxide ion

were in antibonding orbitals and were partly delocalised

in the complex in to orbitals of chromium. Recently

Stomberg105 showed that a different least squares

refinement of the same data gave a value for the 0 - 0

distance of 1.472 + 0.025 A0 , which was not significantly - n different from that in the o2 ion.

Stomberg106 and, Pedersen and Pedersen107 had

confirmed the formula cr05 , of the blue compound by the

x-ray crystallographic study of pyridine complex of blue

compound and revealed the structure of this compound.

( )4 )

They round (ae 1hown in thill tt~N) thnt t'le ohro:~ium

utom, the two peroxy grOup•, and the nitr'Oifen fttOIII or the

pyridine molecule were all nearly oorlnnar, while the

fifth oxyg.,n atom wu.e looated above thie plane.

!.:o Laren nnd Helmholta108 atudilld the or;ratal of

triammino diperoxyohromium Cr(02)2 .) NH) , and described

(as shown in the figure given below) that the chromium

atom wae seven coordinated with a roughly. T-shaped

arrangement of nitrogen atoms around it, the peroxy groups

lay with the 0 - 0 axes in the plane of the downstroke

of T, so that they and one nitrogen atom formed an irregular

plane pentagon around the chromium atom. The 0 - 0 distance

of 1.31 A0 was aporoximately 0.18 A0 less than that of

the peroxide ion71 • The compound was shown to contain

Cr(II), coordinated with the two super oxide ions.

This view was contradicted by the available

magnetic data. Fergusson, Williams and Young109 showed

that the compound contained Cr(IV), coordinated by the

peroxide ions.

Stomberg110 made an X-ray study of the above mentioned

ammonia compound and confirmed the structure as shown

( 35 )

in the ahove figure, but could not say anything over

the controversy of the presence of either Cr(II) or

Cr(IV) in the compound.

(D) Conduetivitl Measurements :

The reaction between chromic acid and hydrogen

peroxide was followed by conductivity measurements by

s9italsky and Kobosev111 • They found during the reaction

that the conductivity of the solution first decreased

sharpely to a value which remained constant for a major

part of the reaction, and then increased to its initial

value as the reaction approached to its completion.

Thus it indicated that the two intermediate compounds

were formed witho~t involving hydrogen ions, whereas the

end product needed hydrogen ions in its formation. These

intermediate compounds had relatively small affinity

constants,

When the above reaction was repeated by Kobosev

and Galbreich112,they found on the basis of the entropy

and thermal data calculation that the reaction was second -2 order, and thus sug~ested the formation of cr2o9 ions

during the reaction.

The conductivity of the pyridine comulex of blue

compound in dimethyl formamide was determined by Fergusson,

Wilki~s and Young11 3 • They proved t~e compound to be a

molecular donor - acceptor comnlex.

( 36 )

Pillai 11 4 decomposed the ethereal blue compound

over water and during its decomposition he measured the

change in conductivity of the aqueous layer with respect

to time. He observed three breaks in the graph plotted

between the chnnge in conductivity and time, and

concluded that the ethereal blue compound had decomposed

in three stages,

Cr2(Cr2010)3 Cr2(cr2o9) 3 •••••••••• (i) t

cr2(cr2o9>3 cr2(cr2o8 ) 3 • • • • • • • • • • (ii)'

and cr2 (cr2o8 )3 cr2(cr2o7) 3 • • • • • • • • • • (iii) •

While in case of the decomposition of the same but ethyl

acetate extracted blue compound, he obaerved two breaks

in the graph plotted under similar conditions. Thus by

these observations. he showed that the blue compound had

decomposed only thro'.tgh two stages,

and

The formation of the compound, Cr2(cr2o8 ) 3 having the

peroxy nature, was confirmed by Singh11 5 and others.

(E) Determination of l.!olecular Weights z

Riesenfeld116 determined the molecular weight of

the potassium salt, K3cro8 in aqueous solution by the

Gr.yoecopic method. He found the different values, 81.81,

68.41, 78.70 and 61.55 of the mol~cul~r weight of the

( )7 )

compound whose theoretical value was 74.3 • He believed

that the variation in the result was probably due to the

decomposition of the compound in the aqueous solution.

The value11 7 obtained tor the molecular weight

of the red ammonium salt, (NH4)3cre8 in 0.3 N ammonia

solution was much higher than the theoretical value.

This was probably due to the lesser dissociation of the

ammonium salt as compared to the dissociation of the

potassium salt. But these results were in agreement with

the formula. (tTH4)6cr2o12 which would have the molecular

weight 67, if the complete dissociation of the compound

was assumed.

Schwarz and Giese (loc. cit.) determined the

molecular weight of the pyridine complex of blue substance

by freezing point method in benzene, nitrobenzene,

tribromo methane and pyridine, and confirmed the uni­

molecular structure. While Rai (loo. cit,) observed the

decomposition or this complex during its dissolution in

pyridine or any other organic solvent and questioned the

reliability of the results.

Finally to summarize the studies made so far on

the constitution of ethereal blue substance. it can be

said that a review of these studies reveals the complexity

ot the problem in the light of various divergent

experimental results obtained by various investigators.

It was Barreswil who for the first time prepared

the ether extracted blue substance and suggested the

( )8 )

Brodie studied the reaction between chromic acid

and hydrogen peroxide, and found that , when chromic acid

was taken in excess 6 gram atoms of 02 were given off.

~~rtinon observed the deepest blue colouration when the

ratio between chromic acid and hydrogen peroxide was 4 : 2,

and he represented the compound by the formula H4cr2o7 •

On the basis of a series of salts prepared with

different bases by causing them to react with blue

substance, Riesenfeld et.al. assigned the formula, Hcro5 to which Wiede also agreed. Rlesenfeld was also of the

opinion that the blue substance possessed the heptavalent

chromium. Glastner supported the formula HCr05 by the

spectrophotometric studies and showed that three molecules

of hydrogen peroxide reacted with two molecules of chromic

acid to give one molecule of the blue substance. He first

believed the monoperoxy nature of the blue substance,

HCr(03)(o2 ) • But later on he made extensive studies

with Steinberg an~abondoned the idea of its monoperoxy

nature.

Schwarz and Giese prepared the pyridine complex of

the blue substance and studied its reactions with acids,

Ag20 and potassium permanganate. The results of these

studies led them to suggest the formula, cr05

for the

ether extracted blue substance. This formula was further

supported by Evans, Glasner and Steinberg on the basis of

( 39 )

spectrophotometric studies. Fergusson, Wilkins, Young

and Griffith by magnetic measurements, and Pederson ~

Stomberg by x-ray crystallographic studies supported the

formula, cr05 •

Recently, Rai suggested a new formula, cr2(cr2o10>3 for the blue substance and showed it in e~uilibrium with

crer08 according to the following equation &

• This formula had also been supported by Pillai, Singh J., Singh s., Rajput, Rai s.s., AWGsthi and Shrivastava. Apart

from these investigators the studies of Patten, RaJnolds,

Reedy, McLaren, Helmholtz, Bohm and Stomberg also established

the presencs of chromium in the lower valency state than

six in the blue substance.

After considering these various formulas, it becomes

very difficult to judge the authenticity of the formula for

the blue substance. Therefore, with a new approach in

mind the author had tried to establish the correct formula

for the blue substance by preparing it in presence of

thiocyanic acid.

Further, although a number of terms such as blue

peroxyohromic acid, blue perchromic acid and blue perohromate

have been found in use in the literature for the ether

extracted blue substance which is prepared by the reaction

of ~02 with an acidified K2Cr2o7 solution, the present

( 40 )

author feels that, since the acidic nature of the ethereal

blue substance has long been abandoned, the compound may

safely be called blue perchromate. With this view the

blue substance has been called blue perchromate throughout

the thesis.

The studies made on the ethereal blue perchromate

have been classified and arranged in the following chapters.

I, The nature and the behaviour of ethereal blue

perchromate prepared in presence of thiocyanic acid, and

of its decomposition products obtained under different

conditions. A Volumetric Study.

II, Constitution of the water decomposition product

of ethereal blue perchromate. A Gravimetric Study.

III, Constitution of the water decomposition product

of ethereal blue perchromate. A StudY with Ion exchang~e

Resins,

IV. Constitution of ethereal blue perohromate and its

water decomposition product. A pH -metric Study,

v. A study of the decomposition of ethereal blue

perchromate in 1ifferent alkalies.

VI. A study of the decomposition of ethereal blue

perchromate in contact with A~O under different conditione.

( 41 )

VII. A study of the infra red apeotra of the complexes

of ethereal blue perchromate with organic nitrogenous

bases.

The results of investigations have been discussed

in "General Discussion".

1 •

2.

( 42 )

R E F E R E N C E S -----------Barreswil L.c.A., Ann. Chim. PhY••• 20, 264(1847)r

ibid, 20, 364 (1848).

Moissan H. , Compt • rend. , 97, 96 ( 1 88 3) •

Goniok, Osschner de, w., Bull. Aoad. Roy. Bel., 175A, 318( 1909) •

4. Riesenfeld E.H., Ber, 41, 3536(1908).

5. Wiede O.F., ibid., 30, 2178(1897).

6. Schwarz R. and Giese H., ibid., 65B, 871(1932).

1. Rai R.c., D.Sc. thesis, Univ. of .P.llahabad, 1962; on the 'Study of the constitution of blue peroxychromic acid.'

a.

10.

11.

12.

13.

14.

15.

16.

17.

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( 46 )

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