Fluid Phase Equilibria 324 (2012) 13 16

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Fluid Phase Equilibria

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EugeneInstitute of T 20016

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Article histoReceived 1 Received inAccepted 14Available on

Keywords:Critical poinFerrocenen-ButylferroBenzoylferr1-Acetylfer

iticalred. od of om (0The ceriva

1. Introd

Ferrocorganommanufacture of polymers with valuable characteristics, in pharma-ceutical and material chemistry and so forth [1]. To our knowledge,the critical properties of ferrocene or its derivatives have neverbeen measured before. The paper gives the critical temperaturesand pressures of ferrocene, n-butylferrocene, benzoylferrocene,and 1-acIn vacuudecompoble at temferrocenecient dewas obseples duripulse-heaunstable

2. Mater

2.1. Mate

The sacial origin

CorrespE-mail a

(A.P. Popov

ties, aivenpropon m

that the purity of ferrocene and n-butylferrocene samples was notchanged or a little changed in the course of measuring the criticalproperties, while the purity of 1-acetylferrocene and benzoylfer-rocene samples was changed signicantly.

0378-3812/doi:10.1016etylferrocene. Ferrocene is a stable enough compound.m, it sustains a temperature of about 500 C withoutsition and even in the air atmosphere ferrocene is sta-peratures as high as 400 C. However, the derivatives of

are not so stable. In the course of our experiments, a suf-composition of 1-acetylferrocene and benzoylferrocenerved (see Table 1). To diminish the degradation of the sam-ng the measurement of the critical properties we used ating method with ultra-low residence times applicable tocompounds.

ials and methods

rials

mples of the compounds investigated were of commer- and used without any further purication. The sources,

onding author. Tel.: +7 343 2678810; fax: +7 343 2678800.ddresses: e-nikitin@mail.ru (E.D. Nikitin), popov@itp.uran.ru).

2.2. Method

The pulse-heating method was developed by us in the earlynineties and since then has been extensively used for measuring thecritical properties of thermally unstable compounds. By now thecritical temperatures and pressures of about 200 substances havebeen measured using this technique. Recently the pulse-heatingmethod was recognized as a standard state technique [2]. In com-parison with the other modern techniques applicable to thermallyunstable compounds [36], the pulse-heating method providesmuch lesser residence times but in general has larger uncertainties.

The method is based on the phenomenon of liquid superheat[79]. In the course of the experiments, the pressure dependence ofthe temperature of the attainable superheat (spontaneous boiling-up) of liquid is measured. The critical point is not only the endpoint on the vaporliquid equilibrium line, but the end point on theline of the attainable superheat as well. Thus, when the pressure inthe liquid approaches the critical pressure, the temperature of theattainable superheat approaches the critical temperature.

The pulse-heating apparatus and procedure have beendescribed in detail in previous publications [2,1013], so only abrief outline is given below. A liquid under study lled a thin-walled

$ see front matter 2012 Elsevier B.V. All rights reserved./j.uid.2012.03.021al point measurement of ferrocene and

D. Nikitin , Alexander P. Popovhermal Physics, Ural Branch of Russian Academy of Sciences, Amundsena Street, 106, 6

l e i n f o

ry:February 2012

revised form 13 March 2012 March 2012line 23 March 2012

t

ceneocenerocene

a b s t r a c t

The critical temperatures and the cr1-acetylferrocene have been measubelow their critical points. A methbeen used. Residence times were frstances in the course of measuring. the critical properties of ferrocene dfrom the experimental data.

uction

ene and its derivatives belong to the sandwich typeetallic compounds. They are used as fuel additives, in

puriare gical protcom/ locate / f lu id

e of its derivatives

Ekaterinburg, Russia

pressures of ferrocene, n-butylferrocene, benzoylferrocene, andAll the compounds studied begin to decompose at temperaturespulse heating applicable to thermally unstable compounds has.03 to 1.0) ms, which resulted in little decomposition of the sub-ontributions of the groups Fe CH and Fe C for the estimation oftives by the method of Marrero and Gani have been determined

2012 Elsevier B.V. All rights reserved.

nd Chemical Abstract Service Registry Numbers (CASRN) in Table 1. Before and after the measurements of the crit-erties, the purities of the samples were determined byagnetic spectroscopy (Bruker DRX 400). Table 1 shows

14 E.D. Nikitin, A.P. Popov / Fluid Phase Equilibria 324 (2012) 13 16

Table 1Purities of compounds used in critical point measurement.

Compound CASRNa Supplier Purity (mol%)

measu

Ferrocenen-Butylfe1-AcetylfBenzoylfe

aChemical a

Teon cuand measwas closestudy. Thscale readon the cu2 103 cliquid. ThthermomSquare potor. Durinwas adjuthin liquineous boa pulse tothe momfrom an aprobe to nected wwas isolalable banwas obsecomputecorresponature of tfrom thetemperatperature whereas middle pwas calcuends and

If the the measpoint of ttemperatthe meltia temperthe tempprecision

Whenstudy, theatmospheapplied tuntil the changingof the attprobe temmay be bdetermining on thea more rature pertuheat for turbation

molas theoachr phurbahe prtempitivitsuredttainmeasnd Tire chod crowhe tr

the

pmco

,

re 1/ectioaporare cormimililippo

100p

h is

1

e fo

0.40

pvp5 or he Fiits de

iterar pre

calcuNisemenBefore

102-54-5 Fluka 99.9 rrocene 31904-29-7 ABCR 99.7 errocene 1271-55-2 ABCR 99.9 rrocene 1272-44-2 Acros Organics 99.0

bstracts service registry number.

p. The pressure outside the cup was created by a pressured by a dial gauge. The full-scale reading of the gauge

to the estimated critical pressure of the substance undere maximum uncertainty of the gauge was 0.15% of the full-ing. Special experiments showed that the pressure dropp walls did not exceed 0.02 MPa. A platinum wire probe,m in diameter and (13) cm in length, was placed in thee probe served simultaneously as a heater and a resistanceeter. The probe was included in a low-inductance bridge.tential pulses were applied to the bridge from a genera-g a pulse the probe was heated. The amplitude of the pulsested in such a way that by the end of it the probe and thed layer near it were heated to the temperature of sponta-iling-up (attainable superheat). The time from the start of

the moment of boiling-up was from (0.03 to 1.0) ms. Atent of boiling-up a probe temperature perturbation arisesbrupt change of the conditions of heat transfer from thethe liquid. The temperature perturbation is uniquely con-ith a voltage perturbation on the probe. This perturbationted with the help of an amplifying lter with a control-dwidth. Then the signal which we called the boiling signalrved on the screens of a digital oscilloscope and a personalr. The bridge was adjusted in such a way that its balanceded to the beginning of the boiling signal. The temper-he probe at the moment of boiling-up was determined

condition of the bridge balance and by the well-knownure dependence of the resistance of platinum. The tem-determined in such a way was the probe-volume average,boiling-up took place on the surface of the probe in itsart. The temperature of boiling-up (attainable superheat)lated taking into account the thermal losses at the probe

the radial inhomogeneity of the temperature eld.compound under study was liquid at room temperature,uring chamber too was at room temperature. If the meltinghe compound under investigation was higher than roomure, the chamber was at a temperature (1015) K aboveng temperature. For this purpose, there were a furnace andature control system in the apparatus, which maintainederature of the compound under study within 1 K. Such a

was enough. the measuring chamber was lled with the liquid under

pressure established in it was somewhat higher than theric pressure. Pulses from the generator were periodicallyo the probe. The amplitude of the pulses was increasedboiling signal was observed on the oscilloscope screen. By

the box resistance from pulse to pulse the temperatureainable superheat at a given pressure was measured. The

low-sureapprvapopert

Ttive sensmeathe athe pmc arequmetthe g

Tfrom

pc =

whecorrthe vties the fthe sby F

A =

whic

=

by th

= Here0.62

Tand rstvapowasand sureperature perturbation in the initial stage of boiling-upoth positive and negative. The sign of the perturbation ised by the competition of two effects. A vapor bubble grow-

probe screens a part of the probe surface, which leads topid increase of the probe temperature (positive tempera-rbation). On the other hand, a growing bubble consumes

evaporation, which causes a negative temperature per-. Our large experience showed that for comparatively

(451.2 totions giveof these vTc were cand the cvalues obbecause tof Filipporing critical constants After measuring critical constants

99.999.496.095.0

r-mass compounds (nonpolymers) at near-critical pres- temperature perturbation was negative. As the pressurees the critical pressure, the properties of the liquid andases come closer and the amplitude of the temperaturetion decreases.essure in the liquid increased step by step until the nega-erature perturbation dropped to the level of the apparatusy (1 103 K). This pressure was taken to be equal to the

value of the critical pressure pmc , and the temperature ofable superheat at this pressure was taken to be equal toured value of the critical temperature Tmc . The values ofmc are always lesser than the true critical properties andorrection. It is an inherent feature of the pulse-heatingonnected with the peculiarities of bubble nucleation andth of vapor bubbles near the measuring probe.ue critical constants of a stable compound were calculatedfollowing equations:

Tc = Tmc

0,

0 and 1/0 are correction factors [10]. To calculate then factors, the thermophysical properties of the liquid and

phase near the critical point are required. These proper-alculated by the principle of corresponding states usingulas given in a previous paper [14]. The formulas containarity parameter of the compound under study suggestedv [15]:

vp(T/Tc = 0.625)pc

(1)

related with the acentric factor[16]

log10

(pvp

(T/Tc = 0.7

)pc

)

llowing empirical equation [15]:

1 0.664 log10 Ais the vapor pressure at reduced temperatures equal to0.7, respectively.lippov parameters and the critical properties of ferrocenerivatives were calculated by an iteration method. For thetion, pmc and T

mc were used as the critical constants. The

ssure of ferrocene at a reduced temperature T/Tc = 0.625lated using the equations suggested by Barkatin et al. [17]lson et al. [18]. Both equations are based on the mea-t of the vapor pressures of ferrocene at temperatures from 523.2) K and (518.8 to 604.2) K, respectively. These equa- a bit different vapor pressures at T/Tc = 0.625; the averagealues was taken. Then the values of A, 0 and 0, pc andalculated. For the second iteration, the Filippov parameterritical temperature and pressure were calculated using thetained after the rst iteration. Two iterations were enoughhe values of 0 and 0 are little affected by the variationsvs parameter. For instance, the Filippov parameter and

E.D. Nikitin, A.P. Popov / Fluid Phase Equilibria 324 (2012) 13 16 15

the acentric factor of ferrocene determined as described above areequal to A = 1.56 and = 0.273. A variation of the Filippov param-eter by 25% causes changes of the critical pressure and the criticaltemperat

The acetylferrobtained not be usboiling teTb = 232

parametedifcult tof ferroce

We usof the ferrrocene acet al. [18tively. Wwe calcuthe estimcontributthe normby this mtions of t(C5H5)Feferroceneequation

ln pvp = B

The paramTmc and thippov paparamete

For caneeded: tation in athe compin one exously [2,1was estimand Seato

The apunstable on the timof boilingstudy in tand its dand 3) cm0.46, andused in tunstable n-butylfedependent* was foand benzthe sampresult thetemperatof 1-acetythe depeing time the experheating t

Table 2Critical temperatures and pressures of ferrocene and its derivatives: experimentaland calculated values.

poun

roceneutylfecetylfzoylfe

3order

and c[23].

perty

K) bar)

Unce

he ue-hears [2

pc are Tccenes of ble a

esul

he cativropere. Ted inerenp-coot bributughh is tal clateeth

able oylferrocene were calculated with these contributions (seee 2). The differences between the experimental and calcu-

critical properties are great enough, especially for the criticalsure of benzoylferrocene. The possible reason for such a dis-ancy may be the fact that the contributions were determinedg only two compounds. The estimation of the contributions canproved when new results of the measurements of the criticalerties of ferrocene derivatives appear.

onclusion

he critical temperatures and pressures of ferrocene, n-lferrocene, 1-acetylferrocene, and benzoylferrocene have beensured. The contributions of the groups Fe CH and Fe C for theation of the critical properties of ferrocene derivatives by theod of Marrero and Gani have been calculated from experimen-ata.ure approximately by 0.2 and 0.02%, respectively.well-known data on the vapor pressures of 1-ocene [19] and benzoylferrocene [20,21] have beenat sufciently lower temperatures than 0.625 Tc and can-ed for the estimation of the Filippov parameter. Using themperature given by Alfa Aesar [22] for n-butylferroceneC/630 mm Hg leads to a suspiciously high Filippovsr A = 2.92 and a low acentric factor = 0.092. Really, it iso imagine that adding the n-butyl side chain to a moleculene would cause the decrease of the acentric factor.ed the following way to estimate the Filippov parametersocene derivatives. The normal boiling temperature of fer-cording to the data of Barkatin et al. [17] and Niselson] is equal to Tnb = (246 2) C and Tnb = 242 C, respec-e took the average value Tnb = 244 C. Using this value,lated the contribution of the molecule of ferrocene foration of the normal boiling temperature in the group-ion method of Marrero and Gani [23]. Then we estimatedal boiling points of the ferrocene derivatives studiedethod. It is a rough estimation because the contribu-

he molecule of ferrocene (C5H5)Fe(C5H5) and the radical(C5H4) differ from each other. The vapor pressure of the

derivatives at T/Tc = 0.625 was estimated by the following:

CT

eters B and C were calculated from the values of pmc ande estimated normal boiling temperature. At last the Fil-

rameters were calculated by Eq. (1). Further the criticalrs were estimated as it was described above for ferrocene.lculating the correction factors two other quantities arehe factor GT ln J/T, where J is the rate of bubble nucle-

superheated liquid, and the ideal gas heat capacity ofound under investigation. The factor GT was measuredperiment with the critical constants as described previ-0] and estimated at 10 K1. The ideal gas heat capacityated using the atomic contribution method by Harrisonn [24].parent critical temperature and pressure of a thermallycompound determined as described above may depende from the beginning of a heating pulse to the moment-up t* due to the decomposition of a compound underhe course of heating. The critical properties of ferroceneerivatives were measured with the help of probes (1, 2,

in length at heating times t* = (0.03, 0.06, 0.11, 0.22, 1.0) ms. Three or four samples of each compound werehe experiments. The compounds investigated by us areat their critical points. In our experiments, ferrocene andrrocene showed no evidence of decomposition, and noce of the apparent critical properties on the heating timeund. The behavior of the samples of 1-acetylferroceneoylferrocene was more complex. The decomposition ofles as a whole occurred in the measuring chamber; as a

purity of the samples was decreased (see Table 1). Theures of the chamber were 375 K and 411 K for the sampleslferrocene and benzoylferrocene, respectively. However,ndence of the apparent critical properties on the heat-was not observed, so for all the compounds investigated,imental data were averaged over all the probe lengths,imes, and samples.

Com

Fern-B1-ABen

TableFirst-atureGani

Pro

Tc (pc (

2.3.

Tpulspape0.03wheferromaterelia

3. R

Tderivcal pbefosentConfgroucanncontbe rowhicimencalcuthe min TbenzTabllatedprescrepusinbe improp

4. C

Tbutymeaestimmethtal dd Tc (K) pc (MPa)

Exptl Calcul Exptl Calcul

785 8 785 3.61 0.10 3.61rrocene 784 12 784 2.18 0.09 2.18errocene 847 13 794 3.28 0.13 2.71rrocene 886 13 873 1.59 0.06 2.34

groups and their contributions for the calculation of the critical temper-ritical pressure of ferrocene derivatives in the method of Marrero and

Fe CH Fe C

2.98074 2.896607.32203 103 1.72874 102

rtainties

ncertainties of the critical constants measured by theting method were discussed in detail in our previous,13,25]. We estimate the uncertainties for ferrocene atnd 0.01 Tc and for its derivatives at 0.04 pc and 0.015 Tc,is the absolute temperature. The uncertainties for the

derivatives are higher than for ferrocene because the esti-the Filippov parameter for these compounds were not ass for ferrocene.

ts and discussion

ritical temperatures and pressures of ferrocene and itses are given in Table 2. To our knowledge, the criti-rties of these compounds have never been measuredhe critical constants of ferrocene were previously pre-

the form of a poster at the 21st IUPAC Internationalce on Chemical Thermodynamics [26]. The well-knownntribution methods of calculating the critical propertiese used for ferrocene because they do not contain theion of ferrum. The critical temperature of ferrocene canly estimated using the Guldberg rule: Tc = 1.5 Tnb = 776 K,close enough to our experimental value. Using our exper-ritical properties for ferrocene and n-butylferrocene wed the contributions of the groups Fe CH and Fe C forod of Marrero and Gani [23]. The contributions are given3. Then the critical constants of 1-acetylferrocene and

16 E.D. Nikitin, A.P. Popov / Fluid Phase Equilibria 324 (2012) 13 16

List of symbolsA Filippovs similarity parameterJ rate of bubble nucleationp pressureT temperaturet* time from the beginning of a heating pulse to the moment

of boiling-up

Greek symbols1/0 correction factor for the critical pressure1/0 correction factor for the critical temperature acentric factor

Subscriptsc critical statenb normal boilingvp vapor

Superscriptm measured value

Acknowledgements

The study was performed in the framework of the ProgramN 2 of the Presidium of the Russian Academy of Sciences underthe support of the Ural Branch of RAS (Project 12-P-2-1008).We are grateful to Prof. Yuri Yatluk from Institute of OrganicSynthesis of the RAS (Ekaterinburg) for analysis of the samplespurities.

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Critical point measurement of ferrocene and some of its derivatives