I
A. J. BARRY, J. W. GILKEY, and D. E. HOOK Dow Corning Corp., Midland, Mich.
Preparation of Arylhalosilanes
0
RGANOPOLYSILOXANE chemistry was industrially based upon the Grignard process in the early 1940's. That versatile process afforded a ready route to the required organochlorosilane intermediates, but raw materials were costly and the large amounts of solvent required resulted in a process of low volume efficiency. Two direct synthetic methods were developed. The first, a result of work done simultaneously at General Electric Co. and The Dow Chemical Co., involved the reaction of methyl and phenyl halides with silicon metal a t 300" C. to produce the corresponding organochlorosilanes (2, 73-76) and the methyl compounds more efficiently than the phenyl. The other direct process, now commercially important for its versatility and efficiency, resulted from work initiated a t The Dow Chemical Co. and continued a t Dow Corning Corp. This work involved high pressure reactions of hydrogen-containing halosilanes and organohalosilanes of the types HSiXs, RHSiX2, and RzHSiX with unsaturated hydrocarbons and benzenoid compounds. The process as applied to the preparation of alkylchlorosilanes has been described ( 3 ) and patented ( 5 ) , and of arylchlorosilanes has been patented ( 7 , 6).
Thermal Reactions in Vapor Phase
The reaction of benzene and trichlorosilane was first tried as a vapor-phase reaction at high temperatures. When mixtures of the two vapors were passed through a n iron tube (3 inches X 10 feet) a t atmospheric pressure, under various temperatures and contact times, and with and without a variety of catalysts, only very small amounts of phenyltrichlorosilane were obtained along with a large amount of by-product silicon tetrachloride and considerable brown, tarry still-residue. Over half the benzene was recovered unchanged. Thus the first approach to the problem was rather discouraging. Thermal Reactions at High Pressures
Preparation of Phenyltrihalosilanes. BENZEKE-TRICHLOROSILAXE, Autoclave reactions at moderately high temperatures and pressures afforded a more successful approach to the synthesis of arylchlorosilanes: CsHs -I- HSiC13
-+
CeHbSiCls
+ HZ
amounts of by-product silicon tetrachloride, characteristic of this series, which is formed by thermal rearrangement of trichlorosilane (77) :
enous pressures in a rotating steel bomb gave appreciable yields of phenyltrichlorosilane and phenyldichlorosilane a t temperatures about 400" C. Pressures ranged systematically from about 1300 p.s.i. a t 350" C. to about 1900 p.s.i. a t 500" c. 'Threshold temperature for the reaction was about 340" C., and yield increased with temperature u p to a limit (Figure 1). However, there is so much scatter in the recorded data (Table I) and in additional data in Figure 1 that a valid linear relationship may not be presumed. The most significant, yet admittedly generous? curve that may be drawn to show yield us. temperature envelops the data, as shown by the heavy line of Figure 1. Thus, phenyltrichlorosilane yield approaches a limit of 1075 grams a t about 450" C. (run 177), or 33.8y0 theoretical (based on consumed reagent). Some adjustment should be made for the phenyldichlorosilane by-product, as this compound represents silylation of benzene and can be converted to useful product by rather simple means. If this by-product is included in the yield plot, the dashed curve of Figure 1 is obtained. Optimum temperature for the reaction is then about 430" C. The pertinent run (KO.178, Table I) shows a yield which is 36,470 theoretical based on consumed trichlorosilane. Allowing for phenyldichlorosilane. total silylation yield becomes 45.3% theoretical. Low yields are reflected in the large
Table 1.
4HSiC13 -., 3SiC11
+ 2 H ? 4 Si
Accordingly, the 3.63 gram-moles of silicon tetrachloride of run 178 is equivalent to 4.84 gram-moles of initial trichlorosilane. Thus more reagent was consumed in the side reaction than was converted into the desired product, true in nearly all of these runs. Small amounts of diphenyldichlorosilane were isolated from the higher boiling residues from these experiments. BEN ZEh'E-TRIBROMOSILANE, The analogous reaction of tribromosilane with benzene was demonstrated by autoclaving a mixture of 3 gram-moles of each for 16 hours at 490" to 510" C. Distillation yielded 202 grams of phenvltribromosilane (0.6 gram-mole), the principal cut of which boiled a t 9 4 " to 99" C. at 2.3 to 2.9 mm. of mercury. A little biphenyl was also produced, and because of its close boiling point it contaminated the distilled product. The analytical data shown in Table 1'11 are compared with theoretical values calculated on the basis of 6% contamination. CHLOROBEN ZENE-TRICHLOROSILANE. It was hoped that chlorobenzene would react with trichlorosilane under less rigorous conditions than benzene and
Reaction of Trichlorosilane with Benzene and Chlorobenzene"
Athough chlorobenzene was more susceptible to reaction, its reduction b y trichlorosilane resulted in lower reaction efficiency
Rim
ilv. TemD.. C.
Still Charge, Grams
HSiCla
Distillation Products, Grams C6H5C6H.sSiClr CsHe SiHC12 Sicla
Residue
Bomb Charge: CoH6, 1402 grams (18 gram-moles); HSiC13, 2460 grams (18.16 gram-moles) PB-181 180 179 178
177
353 378 403 430 454
3763 3772 3804 3643 3635
1917 1698 1060 713 423
249 309 648 617 826
1324 1152 1139 922 909
0 48 127 206 120
48 293 533 999 1075
26
55 33 120 144
Bomb Charge: C6HsC1, 1352 grams (12 gram-moles); HSiCla, 3257 grams (24 gram-moles) PB-133 102 103 135 104 105 136
325 355 375 387 400 425 445
4403 4443 4518 4352 4554 4473 4475
1054 437 236 454 291 349 587
1174 1985 1872 1778 1936 1982 1817
174 30 163 212 228 339 504
513
112 0 0 0 0 0
1027 1624 1696 1668 1745 1565 1053
140 68 128 84 86 85 206
Reaction time, 16 hours: 14.4-liter autoclave.
Such reactions carried out under autogVOL. 51, NO. 2
FEBRUARY 1959
131
1400 I200
1000 v)
L
2
800
(3
a-
i-
600
>
400 200 0
400
350
REACTION
450
500
TEMPERATURE,
OC.
Figure 1. If adjustment i s made for phenyldichlorosilane byproduct, the dashed curve represents phenyltrichlorosilane yield from the benzene-trichlorosilane system REACTION
consequently afford a more efficient synthesis of phenyltrichlorosilane. In another series of experiments chlorobenzene and trichlorosilane were reacted at various temperatures and autogenous pressures (Table I), Optimum reaction temperature was 390' C. (Figure 2). At 300" C. essentially no phenyltrichlorosilane was formed in 16 hours; the only significant reaction occurring was the reduction of chlorobenzene by trichlorosilane to give benzene. Above 400' C. the yield of phenyltrichlorosilane dropped off sharply and the formation of benzene increased markedly as shown in the lower curve. The run a t 387' C. proved the most efficient of the series-product yield
TEMPERATURE,
'C
Figure 2. Above 400' C., yield from the chlorobenzenetrichlorosilane reaction dropped and benzene formation increased represented 3870 of the trichlorosilane consumed and 66y0of the chlorobenzene charged; 23y0 of the latter was reduced to benzene. While chlorobenzene was more susceptible to reaction than benzene, it showed lower efficiency because of its reduction by trichlorosilane as well as increased consumption of the latter accordine " to the reaction:
+ PHSiCl, .--,
C6H5C1
+
+
CeHsSiCla Sic14 Hz In these runs, phenyldichlorosilane
was produced in variable but much smaller amounts than in the benzene reactions. A composite of the distillation residues of a dozen runs at 400' C. was subjected to further fractional distillation, from which small amounts of bis(trichlorosily1)benzene (11.4% of tails), diphenyldichlorosilane (39.4a/o), and biphenylyltrichlorosilane (15.3%) were isolated and identified (Table VII). A trace of chlorophenyltrichlorosilane was indicated. Preparation of Alkaryltrichlorosilanes. Alkaryltrichlorosilanes may be
Reaction of Trichlorosilane with Aryl Halides"
Table 11.
The products were mixtures of meta and para isomers
Aryl Halide
Run
Reaction Time, Hr.
Av. Temp., O
c.
still Charge, Grams
Distillation Products, Grams HSiCla SiCl, Residue
17
BrSiCla CHaCeHs BnSiClz CHa C6H4Si Cla CHsCeH4SiBrClz
+
292 275 81 51
373
18
BrSiCla CHaCsHs BrzSiClz CHaC ~H4SiCla CHaCsHdSiBrClr
235 275 107 64
124
405
42
ClCe&CrHs CzHsCsH1SiCla CzHsCsHs
1253
191
374
29
Cumyl chloride Cumene Cumyl SiCla
132 70 409 100 55 432
373
1316
185
479
26
(C8Es)z m-Biphenyl SiCls p-Biphenyl SiClr
319 176 84
374
1168
102
435
23
(C6HS)Z m-Biphenyl Sicla p-Biphenyl Sicla
329 131 57
12
375
1173
148
328
o-CHaCeH4Br
13
374
1272
131
375
335
p-CHaCsH4Br
12
369
1248
131
288
Chloroethylbenzene
12
375
1210
289
Cumyl chloride
12
375
358
2-Chlorobiphenyl
16
360
4-Chlorobiphenyl
14
6 moles; 2.4-liter autoclave.
INDUSTRIAL AND ENGINEERING CHEMISTRY
si 49 425
p-CHaC6H4Cl
1 32
Grams
CHaCsH4Cl CHaCaHs CHaCsH4SiCla
FCB 283
Bomb charge: aryl halide, 3 moles: "!la,
wt.,
Other Compounds
457
41
+
ARYLHALOSILANES PREPARATION prepared by reaction of the appropriate hydrocarbon with trichlorosilane, but the use of halosubstituted hydrocarbons should permit lower reaction temperatures, as with chlorobenzene, and thus -~ minimize rearrangement on the aromatic I600 nucleus. Table I1 shows three reactions of halotoluenes with trichlorosilane. 1400 Yield in the first reaction was commenI200 surate with that obtained in the analogous preparation of phenyltri1000 chlorosilane. Reduction of chlorotolu4 ene was less than in the chlorobenzene 0 800 d reaction. I n the bromotoluene reacW F 600 tions, the p-isomer showed a higher yield than the o-isomer, but both were far 400 less efficient than the chlorotoluene reaction. 200 Adaptation of this process to the 0 synthesis of substituted arylchlorosilanes, REACTION TEMPERATURE, 'C in general is illustrated by the last four examples of Table 11. Figure 3, Higher yields of phenyltrichlorosilane at lower temperature result I n the preparations of ethylphenylfrom use of boron chloride as catalyst trichlorosilane and cumyltrichlorosilane the hydrocarbons used were mixtures of reflected also in significant quantities of (Table IV). Data from the complete isomers. The products were believed to trichlorosilane, silicon tetrachloride, and series (4)are plotted in Figure 3. be predominantly the meta isomers, methyltrichlorosilane isolated in the Aluminum chloride promoted the although small quantities of higher distillations. About seven times more reaction of benzene with trichlorosilane boiling isomers, presumably para, were residue was obtained than in the benzenea t lower temperatures, producing a also obtained. In the preparation of trichlorosilane system. maximum of about 4.5 gram-moles at biphenylyltrichlorosilane the 0- and pCHLOROBENZENE METHYLDICHLOROSI-345' C. whereas the uncatalyzed reaction chlorobiphenyls gave identical products LANE. In this experiment, 35.1 gramshowed only a trace of product a t this and in nearly the same ratio. moles of methyldichlorosilane and 18.1 temperature. Despite operability at Preparation of Phenylmethyldilower temperature and consequently chlorosilane. BENZENE-METHYLDI- gram-moles of chlorobenzene were heated together in a 14.4-liter steel bomb lower pressure, ultimate yields of this CHLOROSILANE. This general synthetic for 16 hours a t 350" to 360' C. The catalyzed system were not improved over method is applicable to the reaction of product (8.0 moles) corresponded to a the uncatalyzed, nor was by-product methyldichlorosilane with aryl comyield of 29.7% based upon consumed silicon tetrachloride suppressed. pounds. Four runs were made using silane, but it was contaminated with Large distillation residues appeared, benzene and methyldichlorosilane at a phenyltrichlorosilane. Only a trace of and considerable decomposition occurred variety of closely controlled temperatures trichlorosilane was produced, but 3701, during distillation, attributable to cleav(Table 111). Maximum yield of methylof the chlorobenzene charged was reage catalyzed by aluminum chloride phenyldichlorosilane (33.2y0 theoretical) duced to benzene. Thus, methyldiand its complexes in the pot residues. was obtained between 400 ' and 410 ' C. chlorosilane is a more powerful reducing Preliminary flash distillation from alumiProduct yields were generally equivalent agent than trichlorosilane. num chloride afforded some relief as did or slightly inferior to those of the benzeneseparation of aluminum chloride as a trichlorosilane system (compare with Cafalyzed Reactions eutectic with sodium chloride. HowFigure 1) and followed the same trend ever, neither offered a completely clean with temperature. Preparation of Phenyltrichlorosolution to the problem. The product cut was contaminated silane. BENZENE-TRICHLOROSILANEData on boron fluoride catalysis were with phenyltrichlorosilane, and conMX;. To improve the process, catpromising, but a practically important siderable phenyldichlorosilane was isoalyzed systems were investigated. Initial difficulty appeared. While excellent lated. The latter was probably formed work involved Friedel-Crafts catalysts, yields of phenyltrichlorosilane were obfrom dichlorosilane arising from the and a variety of these were used, each thermal rearrangement of the methylover a range of temperatures. All tained, product isolation was complidichlorosilane. This rearrangement is other variables were held constant cated by the presence of phenyldichloro~
(0
-
Table 111.
Reactions of Methyldichlorosilane with Benzene"
Yields were equivalent or inferior to those of the benzene-trichlorosilane system
.
RUK4
PB-121 120 119 118
Av Temp.,
Still Charge,
Grams
HSiCls
CHaSiHC1z
SiClc
CHsSiCls
CeHe
CsHsSiHCln
CsHa(CHa) SiC1zb
Residue
355 380 405 428
3271 3244 3636 2976
149 208 162 124
526 325 286 177
126 0 79 74
357 506 630 416
517 691 369 780
133 237 509 200
55 1 550 602 562
362 364 634 541
c.
Distillation Products, Grams
Bomb charge: CeHs, 1402 grams (18 moles); CHsSiHClz, 2046 grams (17.78 moles). Contaminated with CsHaSiCla.
-
Reaction time, 1 6 hours: 14.4-liter autoclave.
VOL. 51, NO. 2
FEBRUARY 1959
133
Effectiveness of Dow Corning XS-1 as a soil stabilizer i s demonstrated by immersing treated and untreated cylinders of packed damp clay in half inch of water. Untreated sample on the right i s more than 80% disintegrated aftefi one hour fluorosilane and phenylchlorodifluorosilane. hIole equivalent weights of these compounds calculated as phenyltrichlorosilane were included in the recorded product. Because boron fluoride catalysis data kc-ereindistinguishable from those on boron chloride and random halide rearrangement was involved, this system is discussed in conjunction with the boron chloride experiments. Boron chloride (or boron fluoride) was outstanding in catalyzing the reaction of benzene with trichlorosilane (Table 11.. Figure 3). Threshold temperature was lowered to about 240' C., and the \ield curve shows a maximum between 265' and 280' C. Operating pressures were correspondingly lower, Table IV.
varying consistently from about 400 p.s.i. a t 225' C. to 1500 p.s.i. a t 400" C . Yields of phenyltrichlorosilane were significantly better than those obtained without catalyst or with aluminum chloride. Furthermore, production of silicon tetrachloride was suppressed. In contrast to isolable yields of phenyldichlorosilane in uncatalyzed experiments, boron halide-catalyzed runs showed only a little of this by-product. I t was detected in the bomb-product via infrared spectroscopy. Boron halide-catalyzed runs hvere characterized by higher distillation residues, about threefold the amounts observed in uncatalyzed operation (Table IV). However, these residues contain
useful by-products, and their silylation values should be included in any assay of the reaction efficacy. When distillation residues of six runs were combined for a further careful fractional distillation, the following were isolated : phenyltrichlorosilane (8.9y0 of still load); diphenyldichlorosilane (14.070) ; hexachlorodisilylbenzene (1 4.9%) ; phenylpentachlorodisilylbenzene (9.3%) ; remainder, a black tar incapable of further resolution. Identification of these compounds, two of them isolated as both liquid and crystalline isomers, and their characterizations are in Table V I I . The boron-catalyzed system is markedly superior to the uncatalyzed. Evaluation of the best boron-catalyzed run
Catalyzed Reaction o f Trichlorosilane with Benzene" Boron chloride was the outstanding catalyst
Av. .~
Wt., Run
Catalyst
Max. Press.,
Temp.,
Grams
O
c.
P.S.I.
PB-203 AIC13 38 324 BFa 64 305 279 297 BCla 40 251 BCb 39 276 312 313 BCh 44 311 Bomb charge: CsHs, 1402 grams (18 moles) ; Includes 145 grams PhSiClzF.
Table V.
Still Charge. Grams
Distillation Products, Grams Sic14 C8He csHsSiC13
HSiC13 Residue 636 462 3586 851 847 1250 383 3444 289 514 644 1515b 1020 341 1552 111 3384 1108 412 600 166 3400 450 389 585 900 1510 368 475 486 661 1360 3378 1100 380 HSiC13,2440 grams (18 moles). Reaction time, 16 hours; 14.4-liter autoclave.
ceHsSicla/ Sic14 W t . Ratio
1.83 2.95 3.71 3.88 2.80
Catalyzed Reaction of Trichlorosilane with Toluene"
Threshold temperature was lower than in reaction with benzene
Run
Ar. Temp., O C.
Still Charge, Grams
HSiC13
Sicla
966 242 3799 PB-343 438 344 261 3869 374 346 312 3986 a Bomb charge: C H ~ C S H1656 ~ , grams (18 moles); liter autoclave.
Mesic13
Distillation Products, Grams CsHs C S H ~ C H ~CsHjSiCk
232 0 0 420 0 0 565 89 34 HSiC13, 2440 grams (18 moles): BCh,
0 843 0 689 104 714 1.0-1.3% of charge.
CH3CsH4SiC13
Residue
1475 232 1772 443 1330 686 Reaction time, 16 hours; 14.4-
Catalyzed Reaction of Methyldichlorosilane with Benzene"
Table VI.
Reaction temperatures were much lower than in the trichlorosilane reaction with benzene or toluene
av. Temp., Run
O
c.
Still Charge. Grams
Distillation Products, Grams HSiC13
PB-395 144 3343 3332 394 160 3265 393 182 3268 386 203 385 24 1 3242 384 2 74 3221 a Bomb charge: csH6, 1402 grams (18 liter autoclave.
1 34
CH38iHClz
CH3SiCla
(CH3)?SiC12
CsHs
CsHsSiCls
1815 0 0 1295 0 0 95 59 1044 1299 947 38 198 59 60 664 819 39 263 34 0 615 50 250 458 57 677 25 51 187 435 94 698 106 moles) ; CH3SiHClr, 2070 grams (18 moles) ; BCla, 1.0-1.3% of charge. 0 0
INDUSTRIAL AND ENGINEERING CHEMISTRY
C sH5 (CHa)SiClz
Residue
199 427 175 771 2 88 1035 381 761 789 289 1136 Reaction time, 16 hours; 14.40
ARYLHALOSILANES PREPARATION (312) is summarized below: Actual, Potential, % 70 Phenyltrichlorosilane yield Trichlorosilane-basis Benzene-basis Silylation yield Trichlorosilane-basis Benzene-basis Silicon balance, atoms
49.8 69.6
58.0 87.0
56.6 79.2
65.8 98.7
14.38
17.21
15.56
17.60
gram-
Phenyl balance, grammoles
Results in the second column are based on correction of distillation data to account for mechanical losses, particularly in discharging the bomb. Phenyltrichlorosilane yields are based upon reagents consumed ; silylation yields relate the number of siliconcarbon bonds established in all products to mole-reagent consumption. Preparation of Aryltrichlorosilanes. TOLUENE TRICHLOROSILANE - BORON CHLORIDE.Compared with benzene, the general1)- greater reactivity of toluene under onium-ion attack made it a point of interest in the synthesis of aryltrichlorosilanes. The reaction of toluene Lvith trichlorosilane was studied in exactly the same manner as for benzene. Pertinent data are condensed in Table V: and significant trends are plotted in the curves of Figure 4.
-
7
A
6
/ \ I
5
p 4
23 2 I
0 1600
ANALOGOUS BENZENE REACTION
1400 1200 ~ l 0 0 0
a
I
41
I.
ol!
I
,
I200
I
I I
I
--
4-
1
I
I
I
I
1000
TOLUENE REACTON
1
I
W
1
I
I
v)
attacking group can only go ortho to a methyl group on the benzene ring. A mixture of 2.08 gram-moles of mesitylene and 4.0 gram-moles of trichlorosilane were bombed with 0.08 gram-mole of boron trichloride in a 2.4-liter unit, for 15 hours at 308' to 316' C. While the temperature was accidentally higher than intended, the reaction was sluggish and only 0.34 gram-mole of mesityltrichlorosilane was obtained by fractional distillation. I t was isolated as a cut at 142' to 142.5" C. a t 30 mm. of mercury and was identified by proper analytical data (Table VII). I n low-boiling forecuts, 0.34 grammole of xylene was recovered. An 86gramcutboilingbetween127'and 134°C. a t 30 mm. of mercury was identified as xylyltrichlorosilane. Most signifi- . cantly, 0.42 gram-mole of methyltrichlorosilane was found, as expected if ortho-elimination produced the observed xylene and its derivative. This amount is large compared with toluene runs, as mesitylene offers only ortho-sites for reaction. BIPHENYL - TRICHLOROSILANE - BOROY CHLORIDE. Biphenylyltrichlorosilane MESITYLENE-TRICHLOROSILANE-BOROK was made by heating a mixture of 18 CHLORIDE.This system was studied as a gram-moles each of biphenyl and trimore rigorous test of the ortho-eliminachlorosilane, containing 0.5 gram-mole tion postulated for the formation of of boron trichloride, in a 14.4-liter bomb phenyl compounds in the preceding for 16 hours a t 265' to 270' C. The toluene runs; with mesitylene the bomb was incompletely discharged, but 4648 grams of product from it gave o n distillation 2.21 gram-moles of m-biphenylyltrichlorosilane and 3.97 grammoles of crystalline para-isomer. Allowing for 2.16 gram- moles of recovered trichlorosilane, yield was calculated conservatively to be 39.0% theoretical.
Threshold temperature for the reaction was between 222' and 242' C., some 20" C. lower than for benzene reactions. Yield of tolyltrichlorosilane approached a maximum near 260' C., also lower than for benzene reactions. At higher temperatures, yields became progressively lower because of thermal rearrangement of trichlorosilane, reflected in progressively greater amounts of silicon tetrachloride. At temperatures above 285' C., phenyltrichlorosilane, benzene, and methyltrichlorosilane appeared, possibly as products of the scission of an intermediate ortho-adduct (p-elimination) which is discussed later. Maximum yield of tolyltrichlorosilane in this series was 7.86 gram-moles or 53.27, theoretical based upon unrecovered trichlorosilane. However, the highest product to silicon tetrachloride ratio was observed in run 343 near the threshold temperature. Here, the reaction was far short of completion in the 16-hour reaction time a t 242' C., but it proved the most efficient of the series as the 6.54-gram-mole yield represented 60.401, theoretical based upon consumed trichlorosilane.
I
2a
800
a
9 c.
- 600
P
-I
w
5 400 200 200
0 4 02 2 0
250
REACTION300 TEMPERATURE. 350 ' C
400
Figure 4. The optimum reaction temperature for the catalyzed reaction of trichlorosilane with toluene is lower than for its reaction with benzene
I REACTION TEMPERATURE
'C.
Figure 5. The catalyzed reactions of benzene and toluene with methyldichlorosilane were almost identical, both producing high quantities of residue above 240" C.
0 . Benzene reaction
0. Toluene
VOL. 51, NO. 2
reaciion
FEBRUARY 1959
135
Silicone rubber compounds are often mixed in units such as this. Uniformity of the product is a function of mixing intensity and time as well as basic design o f the mixer PHENYLTRICHLOROSILANE- TRICHLOROSILANE-BORON CHLORIDE. Phenyltrichlorosilane (3810 grams), trichlorosilane (2440 grams), and boron chloride (64 grams) were bombed a t 290' to 310' C. for 16 hours. The 5917 grams of material discharged from the reactor contained unreacted trichlorosilane (940 grams), phenyltrichlorosilane (1 354 grams), by-product benzene (57 grams), and silicon tetrachloride (1 132 grams). I n addition, the following compounds boiling above phenyltrichlorosilane were isolated : Yield, Grams (CeHs) ~Sic12 80 rn-ChSiC&SiCh 476 p-ChSiC&SiCh 141 C ~ H ~ S ~ C ~ Z C ~ H ~ S ~ 356 C ~ C13SiCeHaSiClzCsH4Sic13 73
Silicone based rubbers are tested at 60' F. below zero and 575' F. above to demonstrate flexibility
Reaction of methyldichlorosilane with benzene commenced at a much lower temperature (145" to 151' C.) than the corresponding trichlorosilane reaction with either benzene or toluene, but the threshold was much less sharply defined (Figure 5). With increase in temperature, yield of methylphenyldichlorosilane increased to a maximum a t about 203 'C., then decreased a t higher temperatures as redistribution reactions between the desired product and the initial methyldichlorosilane produced progressively more trichlorosilane, phenyltrichlorosilane, methyltrichlorosilane, and dimethyldichlorosilane. Extraordinarily high residues were observed a t temperatures above 240' C. The best attempt a t plotting a product to by-product ratio would relate the sum of the two phenylsilanes (both useful silylation products) to the sum of the two methylsilanes. As plotted against temperature (Figure 5), the curve reaches a peak a t about 203' C., where maximum yield also occurs. The 5.60gram-mole product represents a 44.370 theoretical yield when allowance is made for recovery of 615 grams (5.35 grammoles) of methyldichlorosilane.
absorption spectra were obtained on several of the listed compounds and compared with the curves of Clark and coworkers (9) who studied several species of ring-substituted phenyl silanes. They showed that isomer distinction could be viewed in the 5- to 6-micron region but was particularly resolvable a t longer wave lengths where ortho, meta, and para isomers were distinguished by absorption bands at 13 to 13.5, 12.5 to 13, and 12 to 12.5 microns, respectively. I n this manner, the whole sample of tolyltrichlorosilane obtained by the boron-catalyzed synthesis was shown to be a n equal mixture of meta and para isomers with a trace of ortho possibly present; the low boiling plateau in the table is undoubtedly m-tolyltrichlorosilane. Biphenylyltrichlorosilanes and bis(trichlorosilyl) benzenes were sharply cut in their distillation, and liquid fractions in both cases were pure meta isomers while the crystalline compounds were pure para isomers.
Of the higher boiling material, 520 grams remained . as still residue. The first four compounds were found in the still residues of boron chloride-catalyzed benzene-trichlorosilane reaction products. The last was probably there also, but in amount too small for isolation. Theoretical Considerations The four new compounds are characAn ionic mechanism might best exterized in Table V I I . plain the formation of the products Preparation of ArylmethyldichloroTOLUENE - METHYLDICHLOROSILANEfound. This would first entail thermal silanes. The method just described for BORANECHLORIDE. The reaction of dissociation of trichlorosilane, for exthe silylation of benzenoid compounds toluene with methyldichlorosilane was ample, to give siliconium ions capable of by trichlorosilane may be extended more almost identical in character to the addition to the aromatic nucleus as ingenerally to other chlorohydrosilanes foregoing benzene reaction. Essential dicated : as established by the following work. data are plotted in Figure 5; complete Procedures were identical with those of /S+icl, + H (1) tabular data are reported elsewhere ( 4 ) . HSi C1a
