United States Patent Office Patented Jaxa
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3,073,856 United States Patent Office Patented Jaxa. 5, 1963 2 with a dialkylformamide such as dimethylformamide in 3,073,856 PREPARATION OF ORSANC SECON which several molecules of the latter are present for each COMPéUNEDS of the former and that this influences the course of the Douglas Peter Dodgson, Newport, England, assignor to reaction. Analogous complexes are also formed by di Monsanto Chemicals Limited, London, England, a 5 methylformamide with a wide variety of substituted sili British company con halides, and as these complexes also influence the No Drawing. Filed July 30, 1957, Ser. No. 675,012 behaviour of the SiCl group towards alcohols and phenois Claims priority, application Great Britain July 31, 1956 in such a way that SiOH groups are formed and organic 8 Claims. (C. 260-448.8) halides liberated, this enables the production by analogous O reaction of organopolysiloxanes or silicones. Not all sub This invention relates to the preparation of organic sili stituted silicon halides form these complexes, but those con compounds. which do can easily be recognised by their behaviour to Silicon tetrachloride readily reacts with ethyl alcohol wards dimethylformamide: the complex is partially with replacement of the chlorine atoms by ethoxy groups, ionised in the dimethylformamide solution and the solu and this reaction is used commercially for the manufac 5 tion thus conducts electricity, and also in many instances ture of tetraethyl orthosilicate. the complex can be separated from free dimethylform amide by simple distillation of the latter. SiCl, +4EtOH-Si(OEt) +4HCI A process of the invention is one for the preparation Other organic hydroxyl compounds, for instance higher of a silanol, in which a silicon halide capable of ionisa alcohols, phenols and cresols, react in the same way, 20 tion in a dialkylformamide is treated with an organic given rise to the corresponding silicon esters. The re hydroxyl compound in the presence of a dialkylformamide action proceeds in good yield, and by-products are negli solvent. gible. Moreover, as has been explained above, the hydroxyl It has now been discovered that if the reaction is car groups of the silanol can condense together to give a ried out in the presence of a solvent capable of ionising 25 condensed siloxane containing the siloxane linkage silicon tetrachloride such as dimethylformamide it pursues Si-O-Si. The detailed structure of the condensed silox a different course, and results in products of a different ane largely depends of course on the particular silicon nature. It has been found that although the same reac halide employed as starting material. For instance if the tion occurs to some extent, a second reaction also occurs. hydroxyl compound is ethyl alcohol and the silicon halide In this second reaction chlorine atoms are replaced by is silicon tetrachloride (the material chosen by way of hydroxyl groups and ethyl chloride is produced as by example in the preceding description) or an ethoxychloro product. - - . silane the final siloxane will be a condensed ethoxy silox =SiC1--EtOH-> =SiOH--EtCi ane, actually an ethyl polysilicate. If however the silicon halide is for instance dimethyldichlorosilane a condensed The hydroxyl groups of the silanol formed are reactive 35 siloxane is obtained which contains Si-Me leakages and and tend to condense with one another with elimination is therefore essentially an organopolysiloxane, that is a of water and formation of siloxane linkages and probably silicone. also condense with more chlorosilane or with ethoxy silanes formed by the first reaction, so that there is a com As the ionising solvent dimethylformamide gives excel plex series of subsequent reactions. 40 lent results and is the preferred solvent, although if de diethylformamide.sired other Suitable homologues can be used, for instance In practice the silicon halides used are normally chlo rides, and suitable ones are silicon tetrachloride itself as well as silicon chlorides containing groups as Substituents The ethyl alcohol and water liberated can then take a 45 on the silicon atom, that is to say chlorosilanes. The further part in reaction, the former being available for Substituent groups can be organo groups, for instance the first reaction, and the latter forming siloxanes by alkyl groups such as methyl, ethyl or propyl or aryl hydrolysis of chlorosilane or ethoxysilane. The final groups such as phenyl, or organo-oxy groups, for instance products are thus condensed ethoxy siloxanes (or ethyl alkoxy groups such as methoxy, ethoxy or propoxy or polysilicates) instead of ethyl orthosilicate. 50 aryloxy groups such as phenoxy. Specific examples of Other alcohols and phenols react in a similar manner, substituted chlorosilanes are methyltrichlorosilane, di and it is thus possible to produce condensed siloxanes by methyldichlorosilane, diphenyldichlorosilane, triphenyl the reaction of silicon tetrachloride with alcohols and chlorosilane, diethoxydichlorosilane and triethoxychloro phenols containing no water, while hitherto the formation silane. of condensed materials has required the presence of botia 55 Suitable organic hydroxyl compounds are aliphatic al alcohol and water. As the mechanism of the reaction cohols such as ethyl, propyl, and butyl alcohols, and when alcohol and say dimethylformamide are used is phenols, for example phenol itself, cresols and Xylenols. different from that when alcohol and water are used, the Such hydroxyl compounds may be substituted by other products naturally have somewhat different properties. groups, provided of course they do not interfere with For instance a condensed ethoxy siloxane obtained from 60 the reaction. silicon tetrachloride and pure ethyl alcohol by a process It is preferable to use a substantial excess of the dialkyl of the invention does in general tend to have a better formamide, and the optimum quantity will vary accord stability and a lower viscosity than a material of the Saime ing to the silicon halide used. Where silicon tetrachlo SiO content obtained from silicoil tetrachloride and ride and dimethylformamide are employed, more than 4 aqueous ethyl alcohol. The lower viscosity is useful in 65 molecular proportions of dimethylformamide to one of certain applications, for instance in hydraulic and other silicon tetrachloride is preferable. As hydrogen chloride functionai fluids. given off during the reaction destroys the dimethylform it is beiieved that silicon tetrachloride forms a complex amide, breaking a proportion of it down to dimethyl 3,078,856 4. 3 removed. The ether extract was distilled at a pressure amine hydrochloride and giving rise to formates of the of 13 mm. of mercury with a maximum temperature of alcohol used, these are preferably recovered for recon 180° C. to remove ether, ethanol and any other volatile version to the dimethylformamide starting material. products, leaving a pale amber viscous liquid (23.9 g.). The reactants and solvent can be mixed in any order, This liquid was redissolved in dry ether, filtered and the but excellent results are obtained if the silicon halide and 5 ether removed under reduced pressure. the dialkylformamide are mixed so that the silicon halide The resulting product was an ethyl polysilicate in the can ionise and then the organic hydroxyl compound is form of a clear amber viscous liquid which by analysis added. was shown to contain the equivalent of about 55% SiO2. Example 1 The polysilicate had a viscosity of 240 cs. at 25 C., a Silicon tetrachloride (17 g; 0.1 mole) was added to specific gravity at 25 C. of 1.229 and a refractive index dimethylformamide (73 g; 1 mole) and the slurry was at 25 C. of 1.4137. stirred for 4 hours at room temperature. Excess di Example 4 methylformamide was distilled off from the resulting com This example describes the reaction of ethanol with plex at a pressure of 0.1 mm. Hg, the maximum tem methyltrichlorosilane. perature applied being 60° C. The residual complex Methyltrichlorosilane (3.73 g; 0.025 mole) was added (45.1 g) contained, combined with the silicon tetrachlo to dimethylformamide (7.3 g.; 0.1 mole), the mass being ride introduced, dimethylformamide (27.7 g., 0.38 mole). agitated throughout the addition. To the resulting white To the complex was added ethanol (40 g.; 0.87 mole) slurry there was then gradually added ethanol (8.1 g; and the solution was fractionally disitilled, first at atmos 20 0.175 mole), with agitation. pheric pressure and then at reduced pressure, at a maxi The product was fractionally distilled at atmospheric mum bath temperature of 100 C., giving ethyl chloride pressure up to a temperature of 100° C. to give ethyl (>1 g.;>0.02 mole), ethyl formate (D13 g.:)0.175 chloride (1.31 g.; 0.02 mole) and ethyl formate (3.97 g.; mole), ethanol (20 g.; 0.44 mole) and dimethylformamide 0.06 mole). The residue in the distillation flask was (11 g; 0.15 mole) and leaving a residue (26.7 g.). The heated to 100° C. at 15 mm. to remove volatile materials, residue was extracted with ether; the residue from the ex and then was extracted with ether to give an ether-in traction was dimethylamine hydrochloride (17.5 g.; 0.21 soluble fraction that was mainly dimethylamine hydro mole). Removal of the ether from the extract gave an chloride (4.1 g.), and an ether-soluble fraction (8.1 g). ethyl polysilicate composition (8.1 g). Examination of The ether-soluble fraction was a high-boiling liquid this composition by distillation resulted in an ethyl poly 30 silicate fraction (4.25 g.), B.P. 120-200 C./0.2 mm., condensed siloxane containing S-Me linkages and n20 1.403 and containing an equivalent of 43% SiO2; a Si-OEt linkages, and was essentially a condensed ethoxy second fraction (1.85 g.), B.P. 200-300 C./0.2 mm., siloxane containing some Si-Me linkages.