GB998655A - Electrolytic marking medium - Google Patents

Abstract

3,4 - Dihydroxybetaphenylpropionic acid is prepared by reducing caffeic acid (i.e. the corre sponding acrylic acid) using hydrogen over a palladium on charcoal catalyst. Specification 579,350, 585,739, 641,256, 682,063 and 966,869 are referred to.ALSO:An electrolytic recording medium comprises an impregnated sheet, e.g. of paper, containing at least one compound: <FORM:0998655/D1-D2/1> in an electrolytically conducting solution. In the formulae: Ra, Rb and Rc may be alkyl, aryl, -NH2, -ORe, -O,CO,Re or H; Re may be alkyl, aryl or a carbon chain terminated by carboxyl, amino or other functional group; Rd may be <FORM:0998655/D1-D2/2> -NH-Rj-, or any (-CRfRg-)n group where Rh may be H alkyl or aryl, Rj may be alkylene or arylene (e.g. -CH2-), n = 1, 2, 3.... Rf or Rg may be H, alkyl, aryl, NH2, OH, or other substituent. Specific compounds named are 3, 4-dihydroxyphenylacetic acid, 3, 4-dihydroxy-betaphenylpropionic acid, and 3, 4-dihydroxyamiline-N-methylsulphonic acid. The solution contains an electrolyte, which may be a chloride, bromide or nitrate of sodium, calcium, potassium, lithium, magnesium, rubidium or caesiun. It may also contain: another acid, e.g. sulphuric or citric, to give a pH of 1.0 to 3.5; a stabilizer, e.g. thiourea, an alkyl derivative of thioura or dithiobiuret; an oxidizing agent, e.g. sodium chlorate; and an anti-fringing agent, e.g. monosodium phosphate Specifications 579,350, 585,739, 641,256, 682,063 and 966,869 are referred to.