US1773024A - Process for the pickling of metals - Google Patents

Description

252. COMPOSITIONS,

Patented Aug. 12, 1930 UNITED STATES Examiner ERNEST CHAPMAN AND ARTHUR HILL, BLACKLEY, MANCHESTER, ENGLAND, AS- SIGNOBS T0 IMPERIAL CHEMICAL INDUSTRIES LIMITED, OF LONDON, ENGLAND PROCESS FOR THE PICKLING OF METALS 80 Drawing. Application filed April 12, 1929, Serial No. 354,696, and in Great Britain April 14, 1928.

It is known that thioureas and substitution products of the type in which R represents hydrogen, alkyl, aralkyl or aryl radicles act as inhibitors against the dissolution of metallic iron in pickling and similar processes. This however is an empirically ascertained fact, and, in the present state of knowledge, it is impossible to state the cause of this inhibitory effect or to predict what bodies will and what will not be effective inhibitors in the pickling process. By efiective inhibitor we understand a body which while not retarding the cleansing action of the metal surface, i. e. the removal of metallic oxide or rust by acid, prevents or greatly hinders attack of the metal itself. It is also known that organic compounds containing a mercapto group are effective inhibitors in processes for the pickling of metal. This is disclosed in the British Patent No. 298,390 and the U. S. patent to Chamberlain In the Chamberlain patent there is disclosed under the broad'class of mercapto compounds the species of compounds known as mercapto thiazoles.

We have discovered that this inhibiting function is not confined to the mercapto thiazoles but the general class gf bodies known as th i azole deg ivativesf'af"very excellent inhibitor s against attack of metallic iron or steel by acids and consequently of great value as additions to pickling and similar acid of cleansing baths.

By thiazole derivatives we mean those 7 40 bodies containing the following structural arrangement wherein X represents hydrogen, a group or radicle of simple or complex structure such for instance as CH --C H SH,

Rl\ H or the following group C-R-NH:

asher'eiiiafteimoie fully set forth. In the Chamberlain patent mentioned above there is specifically disclosed mercapto benzthiazole used as an inhibitor, but we have'now Toii'nd that this useful property appears to be possessed by tl 1iazoles,benathiazoles, naphthg thiazoles and anthrathiazoles in general. As an example of typical inhibiting action exercised by dehydrothi9;p ;t0lnidine-or the correspondingprimuline base we mention that i 0.2 per cent by weight (reckoned on the Wei ht of dilute acid used) of either of these su stances be added to 25 per cent sulphuric acid (for cold pickling) or 5 per cent sulphuric acid (for hot pickling), the acid is found not to attack the metal to any appreciable extent during pickling, whilst without thebaiddition the metal is etched very considera We have found that the product from the interaction of sulphur and o-toluidine under conditions sim"1lar-to'those"6btainingin the manufacture of dehydrothio-p-toluidine or primuline can be converted into a form suitable for use as an inhibitor by simple solu tion in 7 0 per cent sulphuric acid.

' For example, we may heat together 7 parts of o-toluidine and 2 parts of sulphur for 6 hours at 185 C. and then for 18 hours at 210215 C. Excess of o-toluidine is removed by distillation, preferably in steam or Du v v o-4,

acid of other strengths.

under reduced pressure. The tarry product, from which water is decanted if necessary, is dissolved in 9 times its weight of per cent sulphuric acid, or in suitable quantities of The solution so obtained is added in small proportion to the pickling acid: e. g., 1 lb. of the solution is sufficient for 4000 lbs. of 15 per cent hydrochloric pickling acid. This proportion may be varied to suit special conditions.

e compositions of the body obtained as above described from otolnidine nay be represented by the conventional formula for dehydrothio-o-toluidine.

but it also contains more highly sulphurized bodies of the primuline type, the formula for which is not definitely known.

' p-toluidine or suitable xylidines, i. e. such as contain a free ortho-position adjacent to the amino group, may be used in place of o-toluidine.

If it is preferred to use an isolated thiazole derivative instead of a solution in sulphuric acid, it ma be diluted with salts such as sodium sulp ate. We have discovered that the inhibiting function is possessed by a general class of compounds containing a certain, structural arrangement, this structural arrangement being different from that of the general classes of compounds heretofore known as inhibitors. In the Chamberlain patent hereinbefore mentioned the inhibiting action was attributed to the presence of the mercapto group and it was not known that the thiazole groupin of certain specific compounds classified un er the broad class of mercapto compounds was involved in the inhibiting action. We have found that compounds possessing the thiazole structure function as inhibitors irrespective of whether or not the mercapto group is present. In this application we claim the compounds possessing this inhibiting action which heretofore have not been utilized in processes of pickling of metals; that is thiazole derivatives containing the following general structural arrangement I bR1 -o-N wherein R represents hydrogen,

/R CH;,-C|Hs,N .,BNH: I

or the following grouping B h-Q e wherein R represents a phenyl residue which may or may not be further substituted with alkyl groups. The present invention is more particularly directed to certain compounds under this general class, namely, the dehydrothiotoluidine bodies.

What we claim-and desire to secure by Let-- ters Patent is:

1. In a process of pickling metal, the step which comprises adding to the pickling acid bath an inhibitor to diminish the attack of the acid upon the metal without hindering the removal of scale or dust, the said inhibitor being a thiazole derivative containing the following structural arrangement wherein R represents hydrogen,

. CE4, l i, N I RNH:

or the following grouping R\N%C R NH:

wherein R represents a phenyl residue which may be further substituted with alkyl groups.

2. A process according to claim 1 in which the thiazole derivative used is a dehydrothiotoluidine body.

3. A process according to claim 1 in which the thiazole derivative used is dehydrothiotoluidine.

4. In a process of pickling metals, the step which comprises adding to the pickling acid bath a solution of a dehydrothiotoluidine body in sulphuric acid.

5. In an inhibitor for metal pickling baths, a new composition of matter comprising a strong aqueous solution of sulphuric acid and the reaction products of sulphur and orthotoluidine dissolved in said strong solution.

In testimony whereof we aflix our signatures.

ERNEST CHAPMAN. ARTHUR HILL.