Patent GB-595854-A (GB)
Title: Improvements in the stabilization of polymerizable aromatic compounds
IPC: C07C17/42
Filed: 1945-05-11
Abstract: In the distillation of polymerizable vinyl aromatic compounds (including vinyl heterocyclic compounds of aromatic character), polymerization is inhibited by the addition of one or more 2 : 5-disubstituted hydroquinones in which the substituents are linked to the hydroquinone nucleus through a carbon atom, with or without other polymerization inhibitors, e.g., hydroquinone or p-tert.-butylcatechol.  Advantageously there may be used a plurality of inhibitors of different boiling points so chosen as to afford protection of the vinyl aromatic compound in all stages of the distillation, i.e., throughout the distilling, fractionating and receiving apparatus.ALSO:Polymerizable vinyl aromatic compounds (including vinyl heterocyclic compounds of aromatic character) are stabilized against polymerization by admixing therewith one or more 2 : 5-disubstituted hydroquinones in which the substituents are linked to the hydroquinone nucleus through a carbon atom, with or without other polymerization inhibitors, e.g. hydroquinone or p-tert.-butylcatechol.  The substituents may be aliphatic, alicyclic, aryl or aralkyl, and may contain other substituents such as halogens or oxygen-containing groups, e.g. ether linkages or hydroxy groups. Specified groups are methyl, ethyl, propyl, butyl (especially tert.-butyl), amyl (especially tert.-amyl), lauryl, stearyl, phenyl, chlorophenyl, dichlorophenyl, tolyl, xylyl, mesityl, benzyl and cyclohexyl.  The inhibitor may be incorporated in the vinyl aromatic compound by direct addition with agitation, by percolating the vinyl aromatic compound through a layer of inhibitor, or by preparing a concentrated solution of the inhibitor in the vinyl aromatic compound and adding this to a larger quantity of the latter.  When distilling vinyl aromatic compounds, especially homologues and substitution products of styrene, it is advantageous to use a plurality of inhibitors of different boiling points so chosen as to afford protection of the vinyl aromatic compound in all stages of the distillation.  The inhibitors may be removed when desired by washing with an aqueous solution of an alkaline material, e.g. caustic soda or sodium carbonate.  A table shows the effect of the addition to an isomeric mixture of nuclear dichlorinated styrenes of 0.25 per cent of 2 : 5-di-p-tolyl-, 2 : 5-di-(phenylethyl)-, 2 : 5-bis - (dichlorophenylethyl)-, 2 : 5 - dibenzyl-, 2 - tert.-butyl - 5 - (dichlorophenylethyl)-, 2 : 5 - di - tert.-amyl- and 2 : 5 - di - tert. - butyl - hydro - quinone, and, for comparison, hydroquinone, chlorohydroquinone, catechol and p-tert.-butyl-catechol, and of the addition of 0.05 per cent of 2 : 5-dibenzylhydroquinone to styrene. The process is also applicable to trichlorostyrene, side-chain substituted vinyl aromatic compounds, e.g. a -methyl- and p-chloro-a -methyl-styrene, nuclear alkylated vinyl aromatic compounds, e.g. p-ethylstyrene, polyvinyl aromatic compounds, e.g. divinylbenzenes, polynuclear compounds, e.g. vinylnaphthalenes and vinyl heterocyclic compounds of aromatic character, e.g. vinylpyridines and vinylthiophenes. Specifications 576,138 and 578,965, [Group III], are referred to.  2 : 5-Disubstituted hydroquinones are obtainable by reaction of benzoquinone, an aromatic hydrocarbon and anhydrous aluminium chloride, of hydroquinone or a mono-substituted hydroquinone, an alkyl, alicylic or aralkyl halide and anhydrous ferric chloride, or of hydroquinone and an olefine in glacial acetic acid with concentrated sulphuric acid, or by reduction of the corresponding quinones.