1584
HERBERTH. ANDERSON AND THOMAS C. HAGER
VOl. 81
[CONTRIBUTION FROM THE CHEMISTRY DEPARTMENT, DREXELINSTITUTE OF TECHNOLOGY]
Organosilicon Fluoroesters
e.
B Y HERBERT H. ANDERSON AND THOMASHACER RECEIVED JUNE26, 1958 Table I lists the boiling points, densities, refractive indices and molar refractions of 20 new organosilicon heptafluoro-nbutyrates, pentafluoropropionates, trifluorqacetates, difluoroacetates and acetates. The average error in calculated molar refractions is 0.40% and the C-F bond refraction is close to 1.850. An empirical equation b.p. of ester = n(0.250)(b.p. of (4 n)(!)(b.p. of acid)-% is the number of alkyl groups attached to silicon, and temperatures are in "K.-fits the R,Si) normal boiling point nf 11 alkylsilicon fluoroesters with an average error of 6" for ethyl, n-propyl and n-amyl derivatives using 0.302 ask; the average error is 3" for phenylsilicon esters using 0.284 as R . Several other methods of calculating boiling points are unsatisfactory. Nine calculated Trouton constants of 26-33, average 29.5, suggest association in organosilicon esters due to the Si-0 bond. These colorless esters all hydrolyze easily, generally have irritating odors, and tend to decompose a t the normal boiling points.
+ -
MgCl and SiCh; they included CHaSiClr, c2HKSiCl,, nIntroduction C~H?SiCla,cyclo-CsH1$XCL and CHsSiCli from Dow CornAuthors of the many papers on organosilicon es- ing Corp., Midland, Mich. Equipment included apparatus ters, known for approximately 100 years, report with interchangeable ground joints, also pycnometers, numerous difficulties, such as long times in prepara- transfer pipets and a micropipet for the usual measuring of the liquid and later titrating the available acidity-phenol tions using sodium acetate, or low yields or the de- red was the indicator for the phenilsilicon esters of percomposition of the They usually report fluoroacids. boiling points under reduced pressure only, and Typically, reflux of 18 mmoles of RSiCla and 70 mmoles thus there is little opportunity for coinparison of of AgOCOR' for 70 minutes in 18-20 ml. of CCl, was followed by filtration and washing of silver salts, next by normal boiling points. distillation of CCld and then by fractional distillation of the Organic fluorine compounds are now easily avail- organosilicon ester, rejecting the lowest-boiling 25%, .takable and of much industrial importance. In the ing the next 45% for study and leaving 30% undistilled. fluorocarbons there is much stability and the com- An average 12.6 mmoles of organosilicoil ester was a yield of 70% and contained a trace of chlorine if any. Because pounds have surprisingly low boiling points, such of the easy hydrolysis, all the measurements of boiling point, as 82.51O for n-C7Fla, while n-C7Hla boils a t 98.43'.* density and refractive index required rapid manipulation in Gradual introduction of fluorine into acetic acid a room where the partial pressure of water vapor did not causes increase in acid strength as the fluorine con- exceed 10 mm. Often a soda-lime absorber was necessary an easily volatile lachrymatory impurity, probtent increases and produces the lowest boiling point to prevent an acid anhydride, from entering the air in the room. in strong trifluoroacetic acid : CHpCOOH, b . r . ably Analysis for silicon consisted of treatment of the com118.1"; highly-toxic CH2FCOOH, b.p. 165 ; pound with a mixture of fuming nitric and fuming sulfuric CHF2COOH, b.p. 134.2"; CF3COOH, b.p. 72.4'. acids in a covered Vycor crucible, with final ignition t o Si02. There is a method of boiling point numbers for Analysis for available acidity included two closely agreeing calculating the boiling points of organosilicon determinations the average of which is in Table I. Discussion chlorides and bromides but not fluorides, iodides or esters.6 General Trends.-In an organosilicon ester of a Known organogermanium esters, closely related perfluoroacid a high fluorine content is associto organosilicon esters, include ( C ~ H E , ) ~ G ~ O C O Cated F ~ , with a comparatively high liquid density, low (C2H6)aGeOCOC2F6 and (C2H&GeOCO-n-CaF~, refractive index and low normal boiling point. Alamong many others.6 though the density of n-CaHSi(OCOCHF& at 20" Both the stability of the fluorocarbons and the appears to be out of line, there is a proper fit in the stability of the triethylgermanium fluoroesters density at the normal boiling point, thus at a comsuggest the desirability of isolation and study of a parable state. Use of the expansion coefficient series of organosilicon fluoroesters, such as that 0.00120 obtained with n-CaH7Si(OCOC2Fs)a and a in the present paper. dilatometer gives these values for the three esters a t the b.p. of each: n-CsH7Si(OCOCHa)a, denExperimental Results sity 0.809 and molar volume 308 ml., n-CaH.iSiTable I lists the boiling points, densities, refractivc in(OCOCHF&,, density 1.076 and molar volume 332 dices and molar refractions of 20 new organosilicon esters, 16 of which contain fluorine. Visible decomposition of 11 ml. (calculated 331 rnl. from the other two values); compounds a t the normal boiling points limits the accuracy n-C3HpSi(OCOCFa)3, density 1.198 and molar of the individual b.p. to fl"or occasionally f 2 ' . These volume 342 ml. The same correction should apcolorless compounds all hydrolyze quite easily and gencrally When compared with have irritating odors. Supercooled liquid CsHsSi(OC0- ply to C&Si(OCOCHF2)3. the corresponding esters the acetates have relaCII&, although fairly viscous, easily allows determination of the density and rcfractive iiidcx as a liquid a t 20"; cyclo- tively high boiling points and refractive indices and C6HllSi(OCOC2Fb)~ supercools very little. low densities. Molar Refractions.--Some explanation is necesExperimental Starting materials included specially prepared silver salts sary for the molar refractions calculated in Table I. of the four fluoroncids, also n-CrHllSiC13made from n-C&hVogel and co-authors list or furnish data that give these satisfactory values for bond refrac(1) A. Ladenburg, Rrr , 6 , 319 (1872). tions used in the calculations in Table I : C X , ( 2 ) R . E. Moritonna, THISJ O U R N A L , 49, 2114 (1927). (3) €I A . Schuyten and others, rbid , 69, 2110 (1917). 1.296; C-H, 1.676; 0-C=O in esters, 4.98; Si(4) C. D. Oliver and others, ibid., 73, 5722 (1951). c , 2.52; Si-0, 1.80; also C B H 6 S i27.61.' , HOW( 5 ) R . N . Lewis and A . E. Newkirk, ibid., 69, 701 (1947). (0) H. H. Anderson, i b i d . , 7 9 , 2089 (1950); 79, 320 (1957).
(7) A. I. Vogel and others, J. P h y s . C h e w . , 6 8 , 174 (1954); A. I.
ORGANOSILICON FLUOROESTERS
April 5, 1959
1585
TABLE I PROPERTIES OF B.p.,
Compound
Found
NEWORGANOSILICON FLUOROESlERS -Mol.
OC.
Calcd.
n-CaH7Si(OCOCHa)a 237 ... n-CaH,Si(OCOCHF*), 230d 217.6 n-C;H7Si(OCOCFa)v 157 161.7 n-CsH7Si(OCOCzFa)a lisd 183.9 n-CaH&(OCOCaFT)r 20Lid 205.7 . .. CgHlISi(OC0CHa)a 2i7jd C~HIIS~(OCOCF#)I 200 ... CgH&i( O C O C P F ~ ) ~ '216 .. . .. C ~ H I I S ~ ( O C O C ~ F243d ~)~ CsHsSi(Oc0CHa)r' 268d .. CeHsSi(OCOCHF& 248d 249.1 Ct.HsSi(OC0CF:), 198 196.5 C~H&~(OCOCZF& 215 217.4 C g H S i ( 0 c 0 C a F ~ ) ~ 241id 237.9 n-C&lSi(OCOCHa)a 255d .,. n-csH~~Si(OcOcFa)a 181d 187.6 n-CsHIISi(OCOC~Fs)r197d 209.9 C2HsSi(OCOC~Fs)3 169 168.9 CnHsSi(OCOC,F7)r I99 190.7 CHsSi(OCOC2Fs); 159 .
.
.
..
d%
1.119 1.440 1.434 1.510 1.584 1.134 1.418
rima
refr.Found
56.16 57.20 57.72 72.71 87.70 68.04 69.61
55.69 56.91 57.99 72.69 88.04 67.59 69.79
1.566 1.3370 99.59 1.200 1.4775 66.92 1.494 1.4290 67.96 1.481 1.3784 68.48 1.546 1.3551 83.47 1.617 1.3495 08.46 1.074 1.4218 65.46 1.363 1.3410 67.02 1.441 1.3267 82.01 1.545 1.3091 68.06 1.624 1.3111 83.05 1.589 1.3033 63.51
99.63 66.54 67.34 69.22 83.80 98.91 65.37 67.59 82.53 67.95 82.88 63.26
...
1.4160 1.3771 1.3277 1.3156 1.3164 1.4442 1.3583
Calcd.
....
...
. ..
-0CORb-
Calcd.
Found
71.3 80.0 82.7 87.3 90.0 61.4 75 3 81.5 85.2 62.7 73.0 76.3 82.3 85.9 64.1 77.4 83.2 89.6 91.8 91.9
71.1 80.2 82.5 87.6 90.5 61.5 75.4
82.0 84.9 62.8 72.9 76.6 81.9 85.7 63.9 77.6 83.6 90.1 92.1 92.0
-Silicone-Cdcd. Pound
11.3 7.9 6.8 5.0 4.0 9.7 6.2 4.7 3.7 10.0 7.2 6.3 4.7 3.8 10.2 6.4 4.8 5.1 4.0 5.3
11.0 7.8 6.6 4.9 3.8 9.8 6.2 4.7 3.4 9.7 7.2 6.3 4.8 3.6 10.2 6.2 4.7 5.1 3.8 5.0
-Distilled
at-
'C.
Mm.
121-122 130-132 82-83 99-100 123-125 126-128 96-98 111-112 128-129 143-146 132-134 95-96 106-107 128-130 122-123 96-97 107-108 100-101 128-129 87-88
12 12
42 41 33 1 11 14 11 1 1 14 11 12 2 20 18 55 47 42
In white light. All compounds are colorless. Average of two close values by titration. Weighed as SO,. DeMeasurements on supercooled liquid; composition occurred during measurement of normal b.p. * Solid of m.p. 46'. m.p. of solid is 36.5'.
ever, a value of 1.44 for the C-F bond refraction is in considerable error and is ~ n a c c e p t a b l e . ~Suitable data on fluorocarbons without hydrogen makes available values of 1.8458 and 1.855O averaging 1.850 as used herein. Another method of obtaining the C-F bond refraction is subtraction of the M R of n-CaH$i(OCOCF3)3from the M R of n-CaH&%(OCO-n-C3F7)3, obtaining 30.05 for 3 CFrCF2- groups, or 10.016 per group; then subtraction of 2.592 for the two C - C bond refractions and finally division by 4 gives 1.856 for the C-F bond refraction directly. Similarly, the corresponding cyclohexylsilicon esters furnish 1.839 and the phenylsilicon esters 1.826 for C-F. All three values indicate an average of 1.84 i 0.01, confirming the value of 1.850 selected aboveasfg Boiling Points.-Two previous methods of calculating boiling points are unsuited for the organosilicon esters in Table I. A general method of boiling point numbers uses the equation
CF3)3,124.82 in n-CaH$i(OCOCFa)a and 3.44 in CeH&(OCOCF&. No average boiling point number can fit all four cases. Moreover, further calculations of boiling point numbers in organosilicon (iso)cyanates and isothiocyanates-with methyl, ethyl and phenyl as the organic groupslaJ4s h o w s that this method is inaccurate. A special method of boiling point increments, such as for the change of C1 to NCO OT C1 to NCS," is of no value with organosilicon esters. An empirical equation, herein supposedly used for the first time
(9) R . D. Fowler and others, ibid., 19, 373 (1947). (10) C . R . Kinney, THISJOURNAL. 60, 3032 (1938). (11) H. H. Anderson and H. Fischer, J . Om. Clicm.. 19, 1296 (1954).
(14) H. H Anderson, ibid., 69, 3049 (1047); 70, 1220 (1948); 71, 1801 (1949);71, 196 (1850). (15) H. H.Anderson, ibid., 64, 1757 (1942). (16) H.H. Anderson, ibid..?4, 2372 (1952).
r3.p. of ester = (n)(0.250)(b.p. of R 8 i ) f (4 n)(k)(b.p. of acid)
-
uses n for the number of alkyl groups attached to silicon and uses temperatures in OK. This equation fits the normal boiling points of l l alkylsilicon fluoroesters with an average error of 6" using 0.302 as k for ethyl, n-propyl and n-amyl derivatives; the -average error is 3" for 4 phenylsilicon esters using B.p. (in 'C.) = 230.144B.P.N. - 543 0.284 as k. Table I lists the calculated b.p.s. of 8 and is adequate for organic compounds,1oalso cer- alkylsilicon fluoroesters and all 4 phenylsilicon tain organosilicon compounds excluding those with fluoroesters. In addition the empirical equation S i S i , Si-0 and Si-F bonding.6 Now, use of the furnishes calculated b.p.'s of 151.3' (actual 153.0') appropriate boiling point numbersbfor Si and for R for (CZHS)$~OCOCF~,'~ 149.0' (actual 155.0") for in RSi" (R is CH3, CsHs, n-C&7 or C6H6) and solv- (C2Hs)zSi(OCOCFa)21s and 146.6" (actual 148.5") ing each equation yields the individual boiling for C2H$3i(OCOCF3)3.12 All calculations involve point number for OCOCFa in four esters to be: later change into O K . of the normal boiling 6.17 in CHaSi(OCOCFo)s," 5.37 in c ~ H ~ s i ( O c 0 -points in "C.: CF,COOH, 72.4; CHF,COOH, (12) H.H. Anderson and G . M. Stanislow, ibid., 18, 1716 (1953). Vogel. 3 . Chcm. Sac., 624, 647 (1948); A. I. Voael and others, ibid.. 531 (1952). (13) G. S. Forbes and H. H. Anderson, THISJOVRNAL, 70, 1043, 1222 (1948). (8) A. V. Grosse and G. H.Cady, Ind. E n g . Chem.. 89, 367 (1947).
1586
HERBERT H. ANDERSON AND THOMAS C. HAGER
134.2; C~FSCOOH,97.0; n-CaF,COOH, 121.0"; (Cd&)rSi, 153.7; (n-CaH7)4SiI 214; (n-CsHll),Si, 318lP; (CsH&Si, 42EL6 No b.p. is available for (CC"1)4Si. This empirical equation does not fit the normal boiling points of esters containing the C H a S i linkage; here the comparatively great difference in size between the CHI and the OCOCzFt, groups may be important. Kopp's data allow approximate calculation of the molar volumes of the alkyl and the ester groups a t the b.p.s., as shown: CHI, 27.5; CzHs, 49.5; n-CaH7, 71.5; n-CbHI1, 115.5; OCOCFa, 69 0; OCOCzFs, 97.4; OCO-n-C4F,, 125.8 ml. The cyclic CeHb, molar volume 93.5 nil., requires a reduction of k from 0.302 to 0.284 for the equation to fit the b.p.s. In addition, this empirical equation does not appear to fit the boiling points of organosilicon acetates. Possible dipole-dipole interactions in the ester groups of the acetates might differ from (17) (1961). (18)
E. A. Kauck and A. R. Diesslin, I n d .
1 3 8 ~ .Chem.,
W.C. Scbumb and others, T H I S JOURNAL,
4% 2332
60, 2486 (1938).
Vol. 81
those in the perfiuoroesters; thus aItered b.p.'s might result. This type of empirical equation also fits the boiling points of numerous alkylgermanium esters-as has been known since April, 1953, and will be demonstrated in a future publication. Use of 0.370 for k in the empirical equation above furnishes satisfactory calculated normal b.p.s. of 182.6' (actual 183') for (C2H6)~GeOCOCF~, 191.7"(actual 189.6") for (CzH6)3GeOCOC2F6, and 200.6" (actual 201.0') for (C2H6)aGeOCO-n-C1F7.* Trouton's Constants.-The following are calculated Trouton constants-molar heat of vaporization divided by the normal boiling point in OK.-for nine esters : n-C3H.iSi(OCOCFa)a,27.4; n-CaH$Si(OCOC2F&, 27.5; n-CaH$i(OCO-n-CaF~)~,31.0; n-C3H,Si(OCOCHFz)3, 33.6; C ~ H ~ S ~ ( O C O C I F S ) ~ , 26.1 ; C Z H ~ S ~ ( O C O - ~ - C31.4; IF~)~ n-C6H11si(OCO, CFa)a,31.6; CH8i(OCOCzF&, 28.2; also, CeHsSi(OCOCF3)a,28.5. An average of 29.5 is consistent with some molecular association, supposedly due to the nature of the Si-0 bond. PHILADELPHIA 4, PA.
