US2666738A - Bright silver plating - Google Patents

Description

Patented Jan. 19, 1954 BRIGHT SILVER PLATING Otto Kardos, Keyport, N. J., assignor to Hanson- Van Winkle-Munning Company,

Matawan,

N. J., a corporation of New Jersey No Drawing. Application September 15, 1950, Serial No. 185,171

' This invention relates; to silver plating and more particularly to the electrod'eposition' of bright silver depositsfrom silver cyanide plating baths.

I have discovered that reactionproducts of ketones, especially of acetone, methyl ethyl ketone and acetonylaoetone "(2,5-hexanedione) .with carbon disulfide and alkali hydroxide, when properly purified, are excellent brighteners for cyanide silver solutions. v 1 i 'Ihave further discovered that these ketonecarbon disulfide reaction products cooperate very strongly with small amounts of Turkey red oil @(sulfonated castor oil), if the concentration of the latter is maintained within rather narrow limits.

Various sulfur-containing compounds such as: carbon disulfide, ammonium thiosulfate, potassium ethyl xanthogenate, thiourea, alkali dithiocarbamates, mercaptobenzothiazole, mercaptothiazole and mercaptothiazoline have been'proposed and used as silver brighteners. Also the simultaneous use of Turkey red oil with potassium xanthogenate and of Turkey red oil with carbon disulfide as addition agents has been proposed.

' 'A' thorough examination of these addition agents, as well as many other sulfur-containing compounds such as: beta -Mercaptoethanol, 2- inercaptoethyl pyridine, ethylene thiourea, dithiobiuret, rhodanine (2 -thiono-4-keto-thiazo1idine), 2,4-diketothiazolidine, thioammeline, dithioammelide, ZA-diamino-6 thio-1,3,5-thiadiazine and various alkali soluble ammonium thiocyanate-formaldehyde resins, showed that the addition of the above agents, alone or with Turkey red oil, did not give as brilliant a silver deposit as the deposit from a silver plating bath containing the ketone-carbon disulfide reaction products. The ketone-carbon disulfide reaction products in a silver plating bath also permitted the use of a wider currentdensity range and the bath was more stable.

The reaction of ketones of the general type RCH2COCH2R and carbon disulfide in the presence of powdered potassium hydroxide has been described by Apitzsch, Ber. 37, 1,599 (1904) 38, 2,888 (1905) and 41,4028 (1908).

I'have extended this reaction to the gamma diketone acetonylacetone (2,5-hexanedione), and have found that the reaction proceeds also in presence of a 50% solution of aqueous sodium hydroxide; slowly for acetone and methyl ethyl ketone, rapidly for acetonylacetone. I have also found that these reaction products are able to react with formaldehyde.

'10 Claims. (01. 204-46) For the application as silver brighteners, it is very important that the sodium sulfide (or hydro'sulfide) formed by this reaction is completely eliminated from the ketone-carbon disulfide reaction products before their addition to the silver plating bath. This is done by acidulating the end product of this reaction withmineral acid, whereby. the ketone-carbon disulfide reaction product precipitates and hydrogen sulfide is formed. The precipitate is then thoroughly washed with water, redissolved'indilute aqueous sodium hydroxide and reprecipitated with acid. This purification of the reaction product by dis: solution in dilute aqueous sodium hydroxide and precipitation with mineral acid can be repeated several times. The final product can be dried in vacuo and powdered. Weaker acids, such as acetic acid, do not precipitate these reaction products. However, after boiling away the hydrogen sulfide, such solutions can also be used as silver brighteners.

A preferred formula for an aqueous silver bath is:

oz./gal. Silver cyanide 8.0 Potassium cyanide 18.0 Potassiumcarbonate r 6.0 Potassium hydroxide 0.4

But obviously this is but one example of many possible bath. formulas- When, to such a bath, 0.02 to 0.04 oz./gal. -of a methyl ethyl ketonecarbon disulfide reaction product, or of an aceto-, nylacetone-carbon disulfide reaction product, were added together with 10 ml./l. of Turkey red oil (50%), excellent silver electrodeposits were obtained in the Hull cell over a wide current density range. But after about one day's standing oruse of the bath, the degree of brightness of the electrodeposits is considerably reduced and the current density range of brightness considerably narrowed and it isv not possible to restore the excellent initial bath performance by addition of ketone-carbon disulfide reaction product. Turkey red oil or other bath components. It has been found that ifonly 0.8 m1./l. of Turkey red oil (50%) is used, together with 0.02 to 0.04 oz./gal. of ketone-carbon. disulfide reaction product, there occurs, on standing of the bath, first an improvement of the bath performance, fol: lowed by a slow decrease of the brilliancy ofvthe silver deposit; but the brightness range is not narrowed. In this case, that is whenonly 0.8 m1./l. of Turkey red oil (50%) have been added, the initial excellent bath performance can be easily restored by the addition of small amounts of the ketone-carbon disulfide reaction product, approximately 0.01 oz./ gal. per week of standing. Addition of only 0.4 ml./l. of Turkey red oil (50%) to a silver bath containing 0.02 to 0.04 oz./gal. of ketone-carbon disulfide reaction product, initially produces matte and streaky silver deposits. An improvement is noticed if the bath has been standing for several hours. The presence of 1.6 ml./l. of Turkey red oil (50%) will, upon standing, gradually narrow the brightening range of the electrodeposits. The limits for the concentration of Turkey red oil, for continuous satisfactory bath performance, are between; 0.4 'rnL/l; and 1.6 ml./l. or preferablyddmk/lj. to 1.2 rnl-./1. of Turkey red oil (50%).

It should be recorded that some of the methyl ethyl ketone-carbon disulfide' reaction products produced excellent silver electrodeposits over'a wide current density range, even in absence. of.

Example 1 22.8 g. (0.2 mol)v acetonylacetone 6,1 g. (0.8 mol) carbon. disulfide 96g. (1.2 mols) aqueous sodium hydroxide solution (50%) were put into a. 'c1'os ed bottle or flask supplied with reflux condenser.

' On occasional shaking, the. two-phase reaction mixture darkened, a moderate heat evolution occurred. and after about 45 minutes the mixture was homogeneous, dark red-brown and fairly warm. The mixture was then "cojole'dto room temperature and diluted with 400 ml. oi Water. 1.2. mols of hydrochloric acid (1:1 by volume) were then slowly added under stirring. An almost black resinous ma'ss'w'a's precipitated and much hydrogen sulfide escaped. The precipitate was powdered, washed with water and redissolved with 0.8 mol of aqueous sodium hydroxide. This solution was then diluted toapproximately 500ml and 0.8-mol of hydrochloric. acid (1:1 by volume) were added under stirring. The dark brown precipitate was filtered off, washed with water and airor vacuum dried. 0.02 'ozz/gal. of this reaction product, when added to the silver bath as described above, gave a semibright silver deposit in the Hull cell up to about: 20 amps/sq. ft. On addition of 0.8 ml./l'. (0.1 fl. oz./gal.-) of Turkey redoil (50%), a brilliant silver deposit was obtained in the Hull cell up to 20 amps/sq. it. On agitation ina beaker, brilliant silver deposits were obtained up to '45 amps/sq. ft.

Addition of only 0.4 ml./'l-. 'of- Turkey red oil (50%) gave at first-a matte irregular silver electrodeposit, and onlyafter several hours standing could fair deposits be obtained. With 1.6- ml./l. of Turkey red oil, the bath showed some deterioration of performance-on standing, and could not be restored to its initial good performance.

1 .In a more dilute bath prepared from 70 'oz./'gal. Silver cyanide 6.0. Potassiumcyanide -11 1.4.0 Potassium, carbonate g g i 4.5,- Potassium hydroxide -1 A oz./gal. Acetonylacetone-carbon disulfide reaction product 0.02 Turkey red oil'(50%) 0.1 fl. oz./gal.

bright silver deposits up to amp/sq. it. could be obtained only with strong mechanical agita tion of the bath.

For the preparation of small amounts of acetonyl-acetone-carbon disulfide-alkali hydroxide reaction product, temperature control is not required as the reaction is moderately fast and exothermic andthe upper temperature range is limited by the boiling point of carbon disulfide. For the preparation of larger amounts of reaction product, strong cooling of the reaction mixture. is required after an initial induction period of about to 60 minutes, so that the reaction does not. become too violent. For highest yields or solid reaction product, final maintenance of the reaction mixture at C. for several hours, before precipitation with acid, is useful.

Example 2 0.2 mol acetonylacetone 0.8 mol carbon disulfide 1.2 mols aqueous sodium hydroxide. solution reacted as in Example 1.

- Then, after dilution to 600 ml, instead of hydrochloric acid, slightly over 1.2 mols of acetic acid-were added. The solution. was boiled down to 400 ml neutralized with potassium hydroxide solution, diluted to 600 ml. and filtered. 8 ml. of, this dark red brightener solution, when added to 1 liter silver bath, produced bright silver electrodeposits up to about 20 amps/sq. ft. in the Hull cell, the brightness of which was further increased by addition, of 0.8: mL/l. Turkey red oil (50%).

On standing, the brightener stock solution deteriorates slowly, apparently by formation of sodium sulfide but can be restored to its initial performance: by acidulation with acetic acid, boiling and neutralization.

Example 3 0.2 mol acetonylacetone 0.8 mol carbon disulfide 1.2 mols aqueous sodium hydroxide solution reacted 'as-i'n Example 1'.

After the. mixture. had become homogeneous, it was cooled, to room temperature and 0.1 mol. (7.5 ml.) of aqueous. formaldehyde (37%) Was added. Anv exothermic reaction occurred, and after about 15. minutes the reaction mass was cooled, diluted andprecipitated as. in Example 1. A black resinous lump. precipitated, was Washed. with water and hardened on standing overnight. It was powdered, dissolved in aqueous. sodium hydroxide, precipitated with. dilute hydrochloric acid. (1:1 by volume). in an amount at least equivalent to, the. sodium hydroxide used, filtered, Washed, redissolvedin aqueous sodium hydroxide and reprecipitated. with hydrochloric acid. After air drying, 19.5 grams of a. light brown powder were obtained. The results obtained with this. addition agent in a. silver bath werethe same as. those obtained with the additionagent'des'cribed iii-Example 1. Similarly effective-addition. agents were obtained by using 1.6 instead of 1.2. mols-of sodium hydroxide, or using 0.2.mo1' of. formaldehydeinsteadof0.1mo1; m 0

, Example 4 14.4 g. (0.2 mol) methyl ethyl ketone 30.5 g. (0.4 mol) carbon disulfide 48.0 g. (0.6 mol) aqueous sodium hydroxide solution (50%) The above was shaken occasionally in a closed bottle for about two weeks, after which time the mixture became homogeneous. Then .7.5' ml. (0.1 mol) of formaldehyde (37%) were added and, after standing forabout 15 minutes, an addition of 300 m1. of water and finally 0.6 mol of glacial acetic acid were made. The solution was heated to drive out all hydrogen sulfide; and after addition of 0.6 mol. of sodium hydroxide it was diluted to 400 ml. 4 ml. of this brightener solu-, tion, when added to 1 liter of silverbath, ploduced brightsilver electrodeposits over a wide current density range. Their brightness was further increased by addition of 0.8 ml./l. of Turkey red oil (50%). p r r Example 5 25 g. (0.35 mol) methyl ethyl ketone 100g. (1.31 mol) carbon disulfide 751g. (1.33 mol) potassium hydroxide (powdered) 1 ml. water tated, which was dissolved in 20 ml. of sodium hydroxide solution (20%), reacted with 15 ml. of

formaldehyde (37 precipitated with dilute hydrochloric acid and, after filtering, redissolved in sodiumhydroxide and precipitated again with hydrochloric acid. A brown powder resulted which, after washing with water and air drying, was used as'an addition agent to' the standard silver bath. 0.04 oz./gal. of this product produced brilliant silver deposits in the Hull cell and in a'beaker at up to 30 amps./sq.'ft. with agitation. Similar brighteners were prepared without the use of formaldehyde. In general, the presence of formaldehyde will facilitatethe formation of the final products in powder form and increase the yield of these reactions.

Example 6 10.5 g. (0.145 mo1) methyl ethyl ketone 19 g. (0.25 mol) carbon disulfide t 22 g. (0.39 mol) potassium hydroxide (powder),

and

7.5,to 25 g. dimethoxytetraglycol The 'above were reacted in a flask under reflux.

The presence of dimethoxytetraglycol accelerated the reaction considerably. After about 15 minutes, the brown reaction product was dissolved in. 200 ml. of water. This solution wasthenacidulated with 25 ml. of glacial acetic Other :batches-='gave brilliant silver deposits only inpresence of small amounts of Turkey red on: Also the presence of Turkey red oil increases the tarnish resistance of: the silver electrodeposits. Here again, with .10. ml./l. of Turkey red oil (50%), the deposits were excellent in the beginning, but'the'current density range over which brightness could be obtained narrowed consider.- ably after afew hours standing of the bath, and the initial wide brightness range could not be restored by any. additions. Withonly 0.8 ml./l. of Turkey red oil (50%) the bath performance .remained fairly stable andcould be completely re-e stored by small periodic additions of ketonee carbon disulfi'de brightener.

Similar addition agents were obtained from acetone instead of methyl ethyl ketone.

The carbon disulfide reaction products of diethyl ketone, methylamyl ketone, mesityloxide and of sodium levulinate (CH3COCH2CHzCOONa) gave somewhat less satisfactory brighteners.

Acetylacetone and acetol reacted very violently with sodium hydroxide (50%) and carbon disulfide, and' were thus not suitable as starting m'aterials. e

As far as the easeof obtaining these addition agents in solid form of reproducible brightening efficiency and in reasonablygood yield concerned, I prefer the 'acetonylacetone-carbon disulfide reaction products as described in Examples 1 and 3'. a V

r I claim:

1. A process for producing bright silver electrodeposits, which comprises electrodepositing silver from an aqueous cyanide silver plating bath containing 0.02 to 0.04 oz./gal. (0.15 to 0.30 g./liter) of the solid, waterand acid insoluble but alkali soluble reaction product of a ketone of the formula RCHzCOCHs, where R comprises a substituent selected from the group consisting of hydrogen, alkyl, acetonyl (CH3COCH2--) and alkali metal carboxymethyl (-CH2COONa,= CH2COOK), with carbon disulfide and alkali hydroxide, this reaction product having been precipitated by addition of a strong mineral acid and freed from alkali sulfide and hydrogen sulfide.

- 2.-A -process for producing bright silver elec trodeposits, which comprises electrodepositing silver from an aqueous cyanidesilver plating bath containing 0.4 to 1.6 m1./l.' of an aqueous solution of Turkey red oil, 50%, and 0.02 to 0.04 oz./gal; (0.15 to 0.30 g./liter) of the solidywaterand acid insoluble but alkali soluble reaction product of a ketone of the formula RCHzCOCHs, where R comprises a substituent selected from the group consisting of hydrogen, alkyl, acetonyl (CH3COCH2) V and alkali metal carb'oxymethyl CH2CO ONa,

CH2COOK)', with carbon disulfide and alkali hydroxide, this reaction product having been precipitated by addition of a strong minera1 acid and freed from alkali sulfide and hydrogen sulfide.

3. A process for producing bright silver'elecf trodeposits, which comprises Lelectrodepositing silver from an aqueous cyanide silver plating bath containing 0.02 to 0.04 ozL/gal. (0.15 to 0.30 g./liter) of the solid, waterand acid insoluble but alkali soluble reaction product of a ketone of the formula RCH2COCH3, where R comprises a substituent selected from the group consisting of hydrogen, alkyl, acetonyl (CH3COCH2) and alkali metal carboxymethyl (CH2COONa, CH2COOK) a withsubstantially two mols carbondisumde per mol carbonyl group and at 1east=oneand-a half mols alkali hydroxideper mol carbon disulfide, this reaction product having :been precipitated by addition ofa. strong mineral acid and freed from alkali sulfide and hydrogen sulfide.

" ILJA process for producing bright-silver electrod'ep'osits, which comprises electrodepositing silver from an aqueous cyanide silver plating bath cbntainingmi. to '1' .6 'mL/i. of an aqueous Solution of Turkey red'oil, 50%, and 0.02 to 10.04 on/gal. (0.15 to. '0.'30"g:/liter)' or the solid, waterand acid insoluble but alkali soluble reactionxproductof a keton'e'ofthe fori'nula RCHiCOCHa, where R comprises a substituent seiect'ed'irom the group consisting of lhydrogemalkyl, acetonyl- (CHYCO C H tone, methyl ethyl ketone and acetone, wi=th-carbon disulztide' and alkalihydroxide, this reaction product having beenprecipitated by addition-oi arcade/so 8. A process for producing bright silver electrodeposits, which comprises electrodepositing silver from an aqueous cyanide.-- silver plating bath containing 0.4 to 1.6 m1 .71. of an aqueous solutionof Turkey red oil, 50%, and 0.02 to 0.04 oz./gal. (0.15 to 0.30 g./liter) of the solid, waterand acid insoluble" but alkali s'oluble reaction product of a ketone, selected from 'a group 'oonsisting of 'acetonyl aeetone, methyl ethyl=ketone and acetone, with '-substantially Ltwo rnols-carbon disulfide' p'er inol carbonyl group and at=least one'and-a half mols alkali hydroxide per mol carbon disulfide; this reaction product: having been precipitated by addition of a strong mineral acid and freed from alkali sulfide and hydrogen sulfide. l

"9. A process for producing bright silver electrodeposits; which (rim-prises "electrodepositing si-l'ver f-roman aqueous 'cyanide silver plating bath containing 0". 02 to 0.'04"oz./gal; '('0.15'*to-0.30

g./liter) of the solid, waterand acid insoluble but alkali soluble reaction product of a ketone, selected from a group consisting of acetonylacetone, methyl ethyl ketone and acetonewith substantially two mols carbon disul-fide per-incl carbonyl group and at least one-anda half mols alkali hydroxide, in the form of a concentrated aqueous solution, per mol carbon disulfid'e. this 1 reaction having been allowed to proceed-between astrons mineral acid and freed from alkali su-lmic nd hydrog n ulfide 6, A proc ess for producing bright silver electrodeposits, which comprises electrodepositing silver. irom :an aqueous cyanide silver; plating bath containing 0.4 to 1.6 n l/l. of an aqueous solution (of, Turkey red oil, 50%, and "0.012 to 0.04 oz ./gal. (0.15 -to.0.30 g ./liter) of the solid, waterand acid insoluble but alkali soluble reaction product of a ketone, selected from. a :gmup consistingiof acetonylacetone, methyl; ethyl .ketone and acetone, with carbon disu-l fide and alkalivhy di xide, t is r act n product havi been pro.

cipitated by addition 0f a strong; ,minera-l; acid and freed fromalkali sulfide and hydrogensultide. 1 l 1 1. A proces .i p ducin bri ht si ver electrodeposits, which comprises electrodepofiting .and acid insoluble but alkali soluble reaction product of a ketone, selected from a group-consisting of acetonylacetone, methyl ethyl ketone and acetone with substantially two mols carbon disulfide per mol carbonyl group and at least one and a half mols alkali hydroxide, in the form of, a -.concentrated' aqueous solution, per mol' carbon disulfide, this reaction having been allowed to proceed between 30 and 50 G.-at least until the initially heterogeneous reaction mixture became homogeneous and this reaction product having been precipitated by addition of a strong mineral acid and freed from alkali sulfide and hydrogen sulfide;

OTTO KARDOS.

References Cited in the file of'this patent UNITED STATES PATENTS Number Name Date 2,110,792 "Egberg et al. Mar. 8, 1938 2,113,517 Powell et a1. Apr. '5, 1938 2,176,668 Egbert; et 3.1. Oct. 1'7, 1939 OTHER REFERENCES Ser. No. 351,241, Weiner (A. P. 0.), published May '18. 1943'. 1

Claims (1)

1. A PROCESS FOR PRODUCING BRIGHT SILVER ELECTRODEPOSITS, WHICH COMPRISES ELECTRODEPOSITING SILVER FROM AN AQUEOUS CYANIDE SILVER PLATING BATH CONTAINING 0.02 TO 0.04 OZ./GAL. (0.15 TO 0.30 G./LITER) OF THE SOLID, WATER- AND ACID INSOLUBLE BUT ALKALI SOLUBLE REACTION PRODUCT OF A KETONE OF THE FORMULA RC2COCH3, WHERE R COMPRISES A SUBSTITUENT SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKYL, ACETONYL (CH3COCH2-) AND ALKALI METAL CARBOXYMETHYL (-CH2COONA, -CH2COOK), WITH CARBON DISULFIDE AND ALKALI HYDROXIDE, THIS REACTION PRODUCT HAVING BEEN PRECIPITATED BY ADDITION OF A STRONG MINERAL ACID AND FREED FROM ALKALI SULFIDE AND HYDROGEN SULFIDE