Patent GB-379373-A (GB)
Title: Improvements in or relating to metal pickling
IPC: C23G1/06
Filed: 1931-05-29
Abstract: Inhibiting agents for use in metal pickling baths are manufactured by heating thiourea or a substituted thiourea with a reaction product of an aldehyde and sufficient ammonia to react substantially completely therewith and thereafter treating the viscous product with an acid until a hard resin is produced.  In an example, two molecular proportions of acetaldehyde are reacted with two molecular proportions of ammonia in solution in an organic solvent, e.g. alcohol, the product is heated with one molecular proportion of thiocarbanilide, the solvent is distilled off, and the viscous resin obtained is heated with one molecular proportion of sulphuric acid. Other condensation products specified are: the sulphuric acid treated reaction products of one molecular proportion of thiocarbanilide with two molecular proportions of butyraldehyde-ammonia, crotonaldehyde-ammonia, heptaldehyde-ammonia, hexamethylenetetramine or a  - ethyl - b  - propylacrolein - ammonia, or of one molecular proportion of thiourea, di - o - tolylthiourea, di - p - tolylthiourea, phenyl - o - tolylthiourea, mono - phenylthiourea, phenylpiperidylthiourea or phenyl-a -naphthylthiourea with two molecular proportions of acetaldehyde-ammonia, and the products obtained by reacting one molecular proportion of thiocarbanilide with two molecular proportions of acetaldehyde-ammonia and treating the product with two molecular proportions of hydrochloric acid, two-thirds of a molecular proportion of phosphoric acid, two molecular proportions of acetic acid or one molecular proportion of oxalic acid.  Other proportions may be used, e.g. the reaction product of one molecular proportion of thiocarbanilide and two molecular proportions of acetaldehyde-ammonia may be treated with one and two-thirds molecular proportions of sulphuric acid.ALSO:As inhibiting agents in metal pickling baths are employed the condensation products manufactured by heating thiourea or a substituted thiourea with a reaction product of an aldehyde and sufficient ammonia to react substantially completely therewith and thereafter treating the viscous product with an acid until a hard resin is produced.  In an example, two molecular proportions of acetaldehyde are reacted with two molecular proportions of ammonia in solution in an organic solvent, e.g. alcohol, the product is heated with one molecular proportion of thiocarbanilide, the solvent is distilled off and the viscous resin obtained is heated with one molecular proportion of sulphuric acid.  Other condensation products specified are: the sulphuric acid treated reaction products of one molecular proportion of thiocarbanilide with two molecular proportions of butyraldehyde-ammonia, crotonaldehyde-ammonia, heptaldehyde-ammonia, hexamethylenetetramine or a -ethyl-b -propylacrolein-ammonia, or of one molecular proportion of thiourea, di-o-tolylthiourea, di-p-tolylthiourea, phenyl-o-tolylthiourea, monophenylthiourea, phenylpiperidylthiourea or phenyl-a -napthylthiourea with two molecular proportions of acetaldehyde-ammonia, and the products obtained by reacting one molecular proportion of thiocarbanilide with two molecular proportions of acetaldehyde-ammonia and treating the product with two molecular proportions of hydrochloric acid, two-thirds of a molecular proportion of phosphoric acid, two molecular proportions of acetic acid or one molecular proportion of oxalic acid.  Other proportions may be used, e.g. the reaction product of one molecular proportion of thiocarbanilide and two molecular proportions of acetaldehyde-ammonia may be treated with one and two-thirds molecular proportions of sulphuric acid.