Patent GB-674153-A (GB)
Title: Improvements in and relating to methods of preparing 2-vinyldibenzothiophene
IPC: C07D333/76
Filed: 1949-06-09
Abstract: 2-Vinyldibenzothiophene is prepared by processes comprising (a) passing a vaporized solution of 2 - (a  - hydroxyethyl) - dibenzothiphene in an inert volatile hydrocarbon solvent over alumina alone or with other metallic oxides, for example oxides of chromium, tungsten, molybdenum or manganese at an elevated temperature and fractionating the product, or (b) forming a solution in a volatile aromatic hydrocarbon solvent of 2-(a  - hydroxyethyl) - dibenzothiophene and vaporizing the aforesaid solution in the presence of heated activated alumina at a temperature of 325 DEG  to 450 DEG  C. and at reduced pressures and fractionating the product, or (c) dehydrating 2-(a -hydroxyethyl)-dibenzothiophene by contact with anhydrous copper sulphate at an elevated temperature and re-crystallizing the product.  In carrying out the vapour phase dehydration according to the preferred method, the carbinol dissolved in an inert solvent such as an aromatic hydrocarbon, e.g. benzene or toluene is fed to a vertical reaction column packed with catalyst pellets maintained at reduced pressure and at a temperature above the boiling point of the carbinol.  The products are fractionated and the desired product may be recrystallized from a solvent such as alcohol or benzene.  The starting material is obtained by acetylating dibenzothiophene with an acetylating agent such as acetic acid or anhydride, acetyl chloride or bromide or ketene to form 2-acetyl-dibenzothiphene in the presence of a Friedel-Crafts agent such as aluminium chloride or bromide or ferric chloride and an inert solvent such as carbon disulphide, nitrobenzene or carbon tetrachloride.  The ketone obtained on hydrolysis is then reduced, e.g. by catalytic hydrogenation using finely-divided platinum, platinum oxide, palladium, copper chromium oxide &c., preferably in a solvent medium and under raised pressure and temperature to give 2-(a -hydroxyethyl)-dibenzothiophene.  In examples dibenzothiophene is heated with acetyl chloride in carbon disulphide with aluminium chloride and 2-acetyldibenzothiophene obtained on hydrolysis, separated from the 2,8-diacetyldibenzothiophene also formed, is hydrogenated using a copper-chromium oxide catalyst.  The 2 - (a  - hydroxyethyl) - dibenzothiophene is dehydrated in examples (1) by passing a benzene solution to a heated column of aluminium oxide pellets and drawing the vapours through the column by a vacuum pump; (2) by heating with anhydrous copper sulphate in the presence of p-tertiary butyl catechol as inhibitor.  Polymerization of the monovinyldibenzothiophene may be inhibited by compounds which inhibit the polymerization of styrene, e.g. catechol and hydroquinone and these may be washed out when desired with dilute caustic solution. 2-Vinyl dibenzothiophene is suitable for use in the preparation of polymers and copolymers useful in the plastics, coating and dielectric arts.  The Specification as open to inspection under Sect. 91, comprises also the use of dehydrating agents such as potassium acid sulphate, zinc chloride and phosphoric anhydride, the preparation of polyacetyldibenzothiophenes, e.g. diacetyldibenzothiophene by further acetylization and the conversion of the latter to divinyldibenzothiophenes.  This subject-matter does not appear in the Specification as accepted.