1098 WALKER, McINTOSH, AND ARCHIBALD : LIQUEFIED

and C7hernica 1 Combination in the Liquejied Halogen Hydrides and Hydrogen Sulphide. By JAMES WALLACE WALKER, DOUGLAS MCTNTOSH, and EBENEZER

ARCHIBALD.

As was indicated in the preceding communication by one of UH, recent investigation points to the conclusion that ionisation is dependent on chemical combination between solvent and dissolved substance, although it is by no means a necessary consequence of the latter. The recent investigation by Steele and McIntosh (Proc., 1903, 19, 223) on the ionising power of the liquefied halogen hydrides for some ordinary electrolytes Bled to the examination in these media of a variety of substances which are not electrolytes in aqueous or alcoholic solution. If rapidly became apparent that results were being obtained entirely in harmony with the considerations set forth in the preceding corn

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HALOGEN HYDRIDES AND HYDROGEN SULPHIDE. 1099

munication, namely, that ionisation is subsequent to chemical combina- tion with the solvent, and that, at least in some instances, the latter phenomenon is to be ascribed to potsntial valence. The method of conductivity measurement suggested itself therefore as a possible one for ascertaining whether, in analogous cases at least, combination had taken place or not. As a very large number of the organic substances, which have been found to yield conducting solutions in these media, contain oxygen, instances mere selected where combination could only occur in virtue of the higher valency of the oxygen atom. Examples of this class are not numerous, being restricted to the type R(OR,),, which includes alcohols, ethers, acetals, and the ethereal salts of some mineral acids. The tendency of aldehydes, ketones, acids, and their chlorides, amides, ethereal salts, &c., to form additive compounds can always be represented, of course, as being due to the presence of a double linking in the molecule, On extending the range of the investi- gation to include substances, which undoubtedly do combine with these solvents, it was found that many of the resulting solutions either did not conduct at all or only to a very slight degree. It was evident therefore that, although this method might give indication of combination when conductivity was observed, absence of the latter property does not exclude the possibility of combination in the act of solution,

A series of observations were also made on solutions of the same organic substances in liquefied hydrogen sulphide. This liquid mas found to be possessed of a remarkable solvent power for nearly all the substances examined in it, but only in a very few instances, and in those cases in which combination undoubtedly occurs, were the solu- tions possessed of much conductivity.

E X P E R I M E N T A L .

The method employed was the ordinary one with Wheatstone's bridge and telephone j about 4 C.C. of the solvent mere placed in a small conductivity cell, and, after establishing the purity of the solvent by a measurement of its resistance, about 4 drops of the liquid or a few powdered crystals of the solid solute were added, and after solution and mixing a reading was again made. The temperature employed varied with the solvent, namely, - looo for hydrogen chloride, - 80' for hydrogen bromide and hydrogen sulphide, and - 50° for hydrogen iodide. It was maintained approximately constant throughout these qualitative measurements by a bath of solid carbon dioxide and ether boiling either under the ordinary or reduced pressure. In the following table, there is placed under the name of the solvent a symbol to designate the extent t o which the solution of the substance named in

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11 00 WALKER, McINTOSH, AND ARCHIBALD : LIQUEFIED

the first column conducts. Thus (+ + +) signifies a very good conductor, (+ + ) fairly good, ( + ) good, ( - +) poor, ( - - +) very poor, and ( - ) a non-conductor.* The letter C placed after the symbol denotes that there was very distinct evidence of the formation of a compound, either by the separation of a solid substance or by the violent action which accompanies solution causing the evaporation of a considerable amount of the solvent. Only in a very few instances is the absence of conductivity to be attributed to insolubility, since the great majority of the substances were seen to be readily soluble in all four solvents. I n the sixth column of the table there is also placed for the purpose of comparison a series of observations made by Rahlenberg and Lincoln (J. Physical Chern., 1899, 3, 19) when using these organic liquids as solvents for ferric chloride.

Toluene ..................... Cumene ..................... Thiophen .................. Pyrrole ..................... n-Ru tyl iodide ............ isoButyl iodide ............ Chloroform.. ................ Benzyl chloride ............ Benzylidene chloride , . . Bromobenzene ............

Ethylene dibromide ......

Formic acid ............. Acetic acid .................. Propionic acid ............ Chloroacetic acid ......... Bromoacetic acid ......... Trichloroacetic acid ...... Cyanoacetic acid ......... Benzoic acid ............... Ethyl acetate ............... Amy1 acetate .............. Methyl propionate. ....... Ethyl oxalate ............... Ethyl malonate ............ Ethyl benzoate ........... Methyl mandelate ........ Ethyl acetoacetate ...... Triethyl borate ........... Ethoxyphosphorous

chloride ..................

.HCI. - -

+ + + + + C .

+ + + + + + - + + - - -

- + f

+ + +

+ + + + i-+

+ +

HI.

-

- + + -

- + -

+ +

+ +

H,S. FeCl,.

* Th.e substances of highest conducting power, designated by the symbol (+ + + ), showed about the aame conductivity as a N/50 aqueous solution of potassium chloride a t 26".

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HALOGEN HYDREDES AND HYDROGEN SULPLIIDE. 1101

Acetyl chloride .......... Acetyl bromide ...........

Acetonitrile .............. Benzonitrile .............. Acetamide ................. Urea .................... Acetanilide .................

Methyl alcohol ........... Ethyl alcohol ............. Ethylene glycol ........... Glycerol .................... Mannitol.. ................. Phenol.. ................... o-Cresol .................... m-Cresol ................... p-Cresol .................... Quinol.. ................... Pyrogallol ................

Ether ...................... Anisole ..................

Anisaldehyde ............ CEnanthaldehyde ........ Furfuraldehyde .......... Benzaldeh yde.. ........... Para-acetaldeh yde ........ Trithioformaldehyde.. .. Acetone ................... Methyl propyl ketone . Acetophenone ........... Phenyl ethyl ketone .... Benzophenone .......... B e n d ...................... Benzoin ................. Amy1 nitrite .............

p - Nitrotolnene .......... o-Nitrophenol ..........

p-Nitraniline .............

Methylaniline ..........

Diethylmiline ..........

Ni trobenzene ............ 0- Nitro t oluen e

m-Dinitrobenzene ......

Picric acid ................ m-N i traniline ..........

..........

Aniline .................. Dimethylaniline ....... Diphenylamine .......... p-Toluidine ............ a-Naphthglamine ....... B-Naphthy lamine .......

-.

HCI.

4- + + + + + + + + +

+ + +

- - +

+ + c. + + c.

+ +

+ + c.

+ + +

+ +

- + - c.

+ + c. -t. +

HRr. 1 HI.

+ + I 1 + I

+ + t

+ + + + + + + + + +

t + t c . +

+ c. + + + + - +

-

-

+ -1- c. + + + c. + + + + + i C.

+ + + + S + + + + + -1- + + + + + -t i- + + + + + + - + -

-

- ('. + + -I- t- + + + + - -

- +

- + - + +

+ + + c.

- +

+ + c.

+ + c. + c. - + + + c'.

-

- + + +

-1- + c. - c. -

+ + + +

- +

- t

+ + c.

- - -

H,S. FeC',.

+ +

+ +

+ + + + + + + 4

-I-

+

- +

+ + + + + +

+ + + + + +

4 t- + + + +

+ + +

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1108 WALKER, McIN'l'OSH, AND ARCHIBALD : LlQUEFIED

IICI.

I

Phenylhydrazine ....... .I Michler's ketone (tetra-

methyldiaminobenzo- phenone). ................. '

Pyridine ..................... '

Piperidine ................. Quinoline ................ ,

Nicotine .................. j Strychnine ................... Azoxybenzene ........... . ' Azobenzene ............... ~

Diisobutylaniine ........ ~

l - !

i-

~

Since the results with hydrogen sulphide are almost uniformly negative they may be disposed of briefly. Four substances which show considerable conducting power in this solvent are pyridine, piperidine, nicotine, and quinoline-all basic substances that certainly do combine with the solvent forming a sulphide, which might be ex- pected to exhibit a certain degree of ionisation in a dissociating medium. The same remark applies possibly to the only other good conductor, acetonitrile, for the nitriles show a distinctly basic tendency. It is remarkable, however, that of al l the other aromatic bases examined only dimethyl- and diethyl-anilines exhibit any con- ductivity and these only feebly. Four other substances show slight conducting power, and they also belong to classes which are capable of reacting with the solvent, namely, aldehydes and ketones. Of all the other types of organic compounds represented in the above list, possibly none shows any tendency to react with hydrogen sulphide, and only three substances show any conductivity, and that but very faintly. They are methyl alcohol, glycol, and ethyl malonate. All three might be represented as dissociating into a positive hydrogen ion and a complex negative one, but there is also the possibility that in virtue of the oxygen atom, which they all contain, the dissociated substance is an additive compound. Prom the results with hydrogen sulphide, we can only conclude that, since a few substances are good conductors in its solutions, the additive compounds with others, if formed, are only very slightly liable to electrolytic ionisation in this medium.

The behaviour of the halogen hydrides as solvents for the same sub- stances is much more varied and interesting than that of hydrogen sulphide. With the exception of the hydrocarbons and their halogen derivatives, it may be stated roughly that all the substances examined containing the elements oxygen, nitrogen, and sulphur behave in one or other of these solvents as fairly good conductors, and even in the

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HALOGEN HYDRIDES AND HYDROGEN SULPHIDE. 1103

class of hydrocarbon the allied substances thiophen and pyrrole are found to be good conductors. They doubtless combine with the solvent to form salts which then undergo ionisation. But even here a peculiar selective property is manifest, for whilst pyrrole is a good conductor in all three solvents, thiophen dissolved in hydrogen iodide does not con- duct, Examples of the same phenomenon are seen in nearly every group of substances examined. A few of the more striking cases are arranged in the following table :

I o-Cresol ........................ Formic acid .................... Propionic acid.. ................ Bromoacetic acid .......... Acetyl chloride ............... Ace tamide ..................... Acetonitrile .................... Anisole,. ........................ Wnanthaldehyde ............ Benzoin ........................

HC1.

- + + + + + + + c + + -t

-I- 4- + + + + + + + +

- _

HCr.

+- I

- -t f + + + + + -1- + + -1- + + + + +

-

In most instances, hydrogen chloride seems to yield solutions of highest, and hydrogen iodide solutions of lowest conductivity, but this is not general, for both o-cresol and bromoacetic acid conduct much better in hydrogen bromide than in hydrogen chloride, and nicotine better in hydrogen iodide than in hydrogen bromide. Further, there is a distinctly selective action between substances of the same type towards one solvent. This might to some extent be anticipated, but it exhibits itself in a somewhat peculiar mamer. For example, the monohydric phenols and the riitrohydrocarbons both conduct well in hydrogen bromide; one might therefore expect the nitrophenols to be even better conductors, but such is not the case ; o-nitrophsnol conducts very little and picric acid not at all in that solvent.

The most interesting problem which suggests itself, however, with regard to these results is the nature of the substance which under- goes ionic dissociation. Walden has attributed most of the instances which came under his observation when using liquid sulphur dioxide as solvent t o an ionisation of the original material, and not to that of a compound between the solvent and solute. This explanation might apply to some of the foregoing instances, but it would lead us beyond the extreme limits of analogy t o apply it in all cases, and assign to such substances as thiophen, pyrrole, ethers, acid chlorides, ethereal salts, aldehydes, ketones, or nitrohydrocarbons a degree of ionisation comparable to that which is found in aqueous solutions of salts,

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11 04 WALKER, MCINTOSH, AND ARCHIBALD : LIQUEFIED

Further, the actual formation of compounds of most of these classes of substances either with the halogen hydrides or with metallic halides is well known and was often indicated during this investigation by a violent reaction on solution, or even by the separation of a solid com- pound. I n some instances where the reaction was particiilarly violent, a considerable amount of the organic substance was added in the hope of isolating the compound formed. For example, the solid methyl mandelate was dissolved in large quantity by hydrogen chloride, but only a syrupy liquid was obtained, which could not be brought to crystallisation at a temperature above that of the freezing point of the solvent, I n the case of ether and hydrogen iodide, however, a solid substance was easily isolated. The explanation of these phenoniena must in harmony with all known facts is, therefore, tha t even the substances containing oxygen unite with the halogen hydrides to form salts, many of which dissociate in the excess of the solvent, Whether those which dissolve, but do not yield conducting solutions, also com- bine with the solvent is one of the many points in this inquiry which requires further investigation. For the present, it is sufficient to re- member that the halogen compounds of some metals in aqueous solu- tion are practically non-electrolytes, whilst those of others are among the best conductors in the same medium.

As was pointed out at the commencement of this communication, the constitution of such additive compounds can in most instances be ascribed to the presence of a double linking pre-existing in the mole- cule. But there are a few cases in which this representation of the structure of these substances is not applicable. Alcohols, phenols, ethers, and two ethereal salts, namely, ethyl borate and ethoxyphos- phorous chloride, can only form additive compounds in virtue of a potential valency or valencies, and in all except the last-named sub- stance the only probable atom to which this property can be attributed is the oxygen atom.

A comparison of the substances which conduct in the halogen hydrides with those which yield conducting solutions when ferric chloride is dissolved in them shows a very great degree of similarity. The only striking exceptions are the ethers, although even anisole manifests some conductivity when ferric chloride is dissolved in it, and has been shown in the previous communication to be capable under the necessary conditions of very considerable ionising power. Now the classes of compounds thus yielding conducting solutions are evidently such as will very likely be found to yield compounds with ferric chloride, since they do so with aluminium chloride. In this case also, conductivity is therefore to be attributed to ionisation following on combination. The same statement applies to many at least of the observations of Franklin and Kraus (Amer. Chern. J., 1900,

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EALOCIEN HYDRIDES AND HPDROGEX SUEPHCDE. 1105

23, 277) on the conductivity of solutions in liquid ammonia. As their o3servations on many organic substances are not given in detail, we have not cited them, but it appears that many of the sub3tances which conduct are just such as are likely to react with the solvent, for example, aldehydes, ethereal salts, phenols, nitrophenols, and possibly dinitrobenzene. I n this connection, it is of interest to recard a few observations which we have made on that solvent. Xethyl, ethyl, n-propyl, and n-butyl iodides, as well as ethyl bromide, shosv a t first, when dissolved in liquid ammonia, only a slight conductivity, wh ich, however, rapidly increases until the solutions conduct quite well. In the case of methyl iodide and ethyl bromide, the formation of an atnine could be easily shown after evaporation of the solution. Carbon disulphide also dibsolves in liquid ammonia to form a solution possessed of high conducting power. Most probably the solution contains in this case ammonium dithiocarbamate. Ether, on the other hayd, shows no conductivity.

The conclusion we feel justified in drawing from these observations is that in at least a great number of cases, if not in all, combination with the solvent is the necessary precursor of ionisation, although such combin2tion does not necessitate ionisation.

If the existence of these compounds between substances containing oxygen and the halogen hydrides is due in any way to their increased stability at low temperatures, comparison of the ammonium and oxonium theories suggests the possibility tha t a t low temperatures such substances as alcohol or ether may add on alkgl iodides to form oxonium iodides. To test this, ethyl iodide was dissolved in ethyl alcohol at - looo, but no conductivity was observed even after an hour. Ether was then added to the solution, but still it remained a non-conduc tor.

Quantitative measurements of the conductivity of some of these solutions have already been made, and some analyses of the solid com- pounds obtained in a few typical instances have already been published (thiq vol., 919).

MACDONALD CHEMISTRY AND MINING BUILDING, MCGILL UNIVEILSITY, 1\IONTREAL.

VOL. LXXXV.

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