Patent GB-624086-A (GB)
Title: Improved manufacture of organo-silicon compounds
IPC: C08G77/00
Filed: 1946-05-21
Abstract: Copolymeric siloxanes produced by hydrolysis and condensation of a mixture of compounds of the type RnSiY(4-n) (n is an integer from 1 to 3, each R is alkyl or monocyclic aryl, and Y is halogen, alkoxy or aroxy) and containing copolymer units with different values of n are treated with an alkali metal hydroxide in a proportion of up to 2 atoms of alkali metal per atom of silicon contained in the copolymer units with the lowest value of n to form salts with these copolymer units, the salts then being separated from the residue containing copolymer units with higher values of n.  The units above referred to are defined as silicon atoms bonded to one, two or three organic radicals.  Specified radicals which R may represent are methyl, ethyl, propyl, butyl, isobutyl, amyl, isoamyl, octadecyl, phenyl, tolyl and benzyl.  The reaction is performed at a temperature below that at which carbon-silicon linkages are broken, preferably below 100 DEG  C. when mono-organo-silicon units are present, or below 150 DEG  C. when they are not.  In separating mono-organo units, the preferred proportion of alkali is between 1 and 2 equivalents per equivalent of mono-organo units present, or less when the mixture contains a small proportion of mono-organo units.  In separating tri-organo units, the proportion is preferably between 1 and 2 equivalents of alkali per equivalent of mono-and di-organo units, or more when there is a preponderance of tri-organo units in the mixture. Mono-organo silicon salts may be crystallized or separated as an aqueous solution from the residues containing di- and/or tri-organo-units.  A solvent for the non-salt-forming portion of the mixture, e.g. ether, may be added.  Di-organo salts which are relatively stable in aqueous solutions containing less than 3.33 mols. of water per mol. of alkali may be separated by decantation or filtration from the tri-organo units which form an oil phase. Addition of a lower alcohol, e.g. ethyl alcohol to the aqueous solution helps in this instance.  Alternatively, the tri-organo units which form a disiloxane may be separated by distillation. The salts, hydrated or after-dehydration may be reacted with organo chlorsilanes or tetrahalo-silanes to form siloxanes, or may be acidified to produce a siloxane or with excess acid preferably in the presence of a solvent for the product, a silanol.  In the examples: (1) a copolymer was produced by hydrolysis and condensation of methyl triethoxysilane, dimethyl diethoxy silane and trimethyl ethoxysilane. Alcohol and hexamethyl disiloxane produced were distilled off.  The residue was warmed to 70-80 DEG  C. with caustic soda solution and cooled. The product was heated under vacuum and tri-substituted siloxanes distilling off were condensed in a dry ice trap.  Water was added to the solid powdery residue, the mixture warmed and allowed to separate into oil and aqueous phases.  The aqueous phase was saturated with ether and dimethyl siloxane was obtained from the ethereal extract and the oil phase.  Monomethyl material was recovered from the salt solution by adding excess HCl in presence of benzene.  Example (2) employs a smaller proportion of alkali and different proportions of water.  Example (3) employs still less alkali and separates the mono-organo silicon units as a salt from the di- and tri-organo units.  Example (4) is similar. Example (5) employs an oily copolymer from mono-methyltrichlorosilane and dimethyldichlorosilane, treats it with caustic soda and filters off the solid sodium salt of the monomethyl silicon units, leaving an oil of greater viscosity.  In example (6) a siloxane (CH3)3SiO[(CH3)2 SiO]4 Si(CH3)3 was refluxed with caustic soda, water and ethyl alcohol.  Hexamethyldisiloxane was then removed by distillation leaving a residue mainly of NaO[(CH3)2SiO]2Na.  Example (7), a copolymer containing diphenyl methyl silicon and diphenyl silicon units was treated with caustic soda and petroleum ether and methanol. Petroleum ether solutions of [(C6H5)2CH3Si]2O were separated from the aqueous phase containing NaO[(C6H5)2SiO]2Na.  Example (8), an oil consisting of HO(C6H5.CH3SiO)3H was purified from contaminating tri-organo silicon material by the process.  Example (9), a copolymer from ethyl trichlorsilane and ethyl phenyl dichlorsilane was separated into phenyl ethyl siloxane and a salt which on acidification yielded a monoethyl siloxane.  Example (10), mixed monomethyl and dimethyl ethoxy silanes were hydrolysed and treated in one step with caustic soda. Example (11), the process was applied to a copolymer from phenyl silicon trichloride and phenyl methyl silicondichloride.  Example (12), dimethyl siloxane was freed from contaminating monomethyl silicon units.  According to the Specification as open to inspection under Sect. 91, R in the above formula may be any monovalent hydrocarbon radical.  This subject-matter does not appear in the Specification as accepted.ALSO:Copolymeric siloxanes produced by hydrolysis and condensation of a mixture of compounds of the type RnSiY(n-4) (see Group IV (a)) (n is an integer from 1 to 3, each R is alkyl or mono-cyclic aryl and Y is halogen, alkoxy or aroxy) and containing copolymer units with different values of n are treated with an alkali metal hydroxide in a proportion of up to 2 atoms of alkali metal per atom of silicon contained in the copolymer units with the lowest value of n, to form salts with these copolymer units, the salts then being separated from the residues containing copolymer units with higher values of n.  Tri-organo substituted silicon units may be recovered from the mixture as hexa-organo disiloxanes.