GB600328A - Corrosion inhibition and anti-corrosion packaging - Google Patents

Abstract

Volatile compounds having a nitrite ion which are used as water-corrosion inhibitors are composed mainly of organic nitrogen base nitrites particularly the salts thereof having a vapour pressure in excess of 0.0002 mm. Hg at 21 DEG C., and preferably in excess of 0.001 mm. The organic bases may be primary, secondary and tertiary amines, and quaternary ammonium bases, including pyridium bases, which have basic diisociation constants close to that of nitrous acid which equals 4 X 10-4 at 18 DEG C. Numerous examples are given of suitable bases. The salts are prepared in most cases by stoichiometric reaction of an organic base with nitrous acid. As examples: (a) the hydrochloride of the base is mixed with sodium nitrite dissolved in a liquid in which the inhibitor salt formed by double decomposition is insoluble; (b) hydrogen chloride gas is passed through an acetone solution of the base, and silver nitrite is added to form an acetone solution of the solution of the nitrite of the base and insoluble silver chloride, the nitrite being purified by recrystallization; (c) concentrated H2SO4 is added slowly to 50 per cent by volume aqueous solution of acetone in the presence of the nitrogen base and in excess of sodium nitrite. The salt is purified after filtration; (d) an aqueous solution of the base is acted upon by the stoichiometric amount of H2SO4, and thereafter adding a stoichiometric amount of sodium nitrite. The sodium sulphate is precipitated out by adding 2 to 5 volumes of acetone, and the nitrite purified. The Specification contains a list of nitrites prepared by the above methods and gives their vapour pressures at 21 DEG C. Dialkyl amine nitrite, oxazine nitrite, and morpholine nitrite are specifically claimed. Other bases for preparing nitrites to act as inhibitors are the isologs of ammonium which have the general formula RXHy, where R is an organic radical which may be alkyl, cycloalkyl, aryl, alkaryl, or heterocyclic. X is an element selected from phosphorous, arsenic, antimony, carbon, oxygen, sulphur, selenium, tin and iodine, and y is an integer from 2 to 4 depending on the valency of X. Trimethylsulfonium nitrite is an example of this series. Also organic esters of nitrous acid having the general formula R-O-NO, and thionitrites R-S-O-NO, where R is an organic radical, may be used. The manner in which the nitrites are used is described in the abridgment for Group XVII. Specification 20340/47, as open to inspection under Sect. 91, is referred to.