US2169576A - Method of making copper phosphate - Google Patents

Description

Patented 15, 1939 UNITED STATES PATENT orric 2,169,576 I METHOD or MAKIN corral; PHOSPHATE Charles Booth and Herbert J. Krase, Anniston,

Ala, assignors, by mesne assignments, to Monsanto Chemical Company, a corporation of Delaware No Drawing. Application June 18,1936,

' Serial No. 85,886

5 Claims.

This invention relates to a copper containing fungicide-and method of making the same.

One' of the objects of thepresent invention is the provision of a process for making a copper phosphate fungicide by electrolytic dissolution of metallic copper. A further object is the provision of asafe and efficient fungicide.

We have found that if a copper anode, together with a cathode made either of copper or an inert material be immersed in a solution containing sodium phosphate and sodium sulfate and a suitable direct current be passed through said electrodes, that a copper phosphate-sodium phosphate complex will be precipitated. in the electrolyte invery finely divided form. This operation may be made continuous by continuously removing the precipitated copper-sodium phosphate complex from the solution and-continuously replenishing the electrolyte. According to our invention it is possible to operatethe cell without diaphragms, thus simplifying the operation con-' siderably. v In previous work on the production of copper phosphate by electrolysis of copper anodes it has been proposed to utilize an electrolyte containing chlorine compounds, particularly sodium perchlorate (German Patent 91,707). Furthermoreit has, hitherto been found necessary to utilize diaphragms surrounding the cathode. For continuous production by the electrolytic methodwe have found that chlorine compounds are undesirable in the electrolyte, particularly when preparing copper phosphate since the presence of such compounds causes the formation of a layer or coating over the anodes which in time increases the-resistance of the cell. The use of chlorate in the electrolyte in a short time builds and relatively high efliciencies obtained. For

reasons already stated it is desirable that the chlorine content of the electrolyte either as chlorine ion or as chlorate ion be relatively low. By way of example we give the following description of one method ofc rryinz out'our in-'- vention:

An electrolytic cell having copper anodes and cathodes is connected to a suitable source of direct current. The current density used may be varied between 15 and amperes per sq. ft. of

anode area, however, for most satisfactory opera- 5 tion, we prefer to operate in the neighborhood of 27 to 30 amperes per sq. ft.

The electrolyte is a dilute solution containing sodium sulfate, disodium phosphate and monosodium phosphate. we have obtained satisfac- 10 tory results using a solution containing 4.5% of Na2SO4 and 0.5% of a mixture of Na2HPO4 and NaHzPOr, the proportions of the latter two salts being such as to give a pH between 5.0 and 8.0.

While the composition of the product is sub- 15 stantially' unchanged between these last enumerated pH values,-for most satisfactory operation we prefer to operate withan electrolyte containing the above mentioned salts, the sodium phosphates being therein proportioned so as to 20 give a pH between the limits of 6.0. to 6.4, whichelectrolyte it will be recognized issomewhat on the acid side of neutrality. During operation the electrolyte tends to-become more basic, which condition is corrected by the regulated addition 25 of phosphoric acid to the-electrolyte, During operation the temperature of the electrolyte is maintained at approximately 30 C.

' The product of our process is a double salt of tribasic copper phosphate and disodium phos- .phate. The formation of this compound therefore withdraws sodium phosphate from the electrolyte which compound must be replaced. We

' find it necessary to add disodium phosphate in addition 'to the phosphoric acid already men- 35 tioned to the electrolyte in' order to keep the sodium phosphate contentof the electrolyte substantially constant.

The formation of the copper phosphate-sodium phosphate complex occurs as a light blue, very finely divided precipitate in the electrolyte. For

continuous operation we therefore remove continuously a portion of the electrolyte containing the suspended product, pass the same through a filter press and return the filtrate to the elec'- trolytic cell. The filtrate returned to the cell is caused to agitate the electrolyte to prevent the copper phosphate from settling out on the bottom. The filter cake in the press is washed, then removed from the press and dried. It may then be finely ground for use as a fungicide, or as an ingredient thereof.

The product as produced by our process has a composition corresponding to the formula:

neighborhood of 6. It is a light blue powder insoluble in cold water and when ground to a size suitable for use in fungicidal preparations it has a particle size varying from 2 to microns. The bull: density varies between 10 and 15 lbs. per cubic foot and usually is in the neighborhood of 12 to 13 lbs. per cubic foot. This is considerably less than the density of copper phosphate as produced by the reaction of' copper oxide and phosphoric acid the latter having been found to have a bulk density of 50-53 lbs. per cubic foot when ground to thesame degree of fineness as the product produced by the present process.

The electrolytic product as herein prepared consists of agglomerates of crystals of the copper phosphate complex, over 99 per cent of the ag-' .crons 17% between and 12 microns and 20% The electrolytic less than 12 microns in size.

" product as herein produced is. also distinguished from the product produced by the reaction of copper oxide and phosphoric acid in that the latter has bulk density approximately foultimes that of our product.

The copper phosphate-sodium phosphate complex as produced by our process normally carried in the neighborhood of 6 molecules of water of crystallization. By heating the complex we are able to lower the amount of contained water of crystallization to any desired degree and indeed we may make a susbtantially dehydrated product merely by heating to the, dehydrating tempera- 4o ture.

We may also produce .tribasic copper phosphate: C113(PO4)2 by leaching the copper-sodium phosphate double salt with hot water. The sodium phosphate may be removed in whole or in part. The tribasic copper phosphate thus produced is of low bulk density and may be used as an ingredient of fungicides in the usual manner.

The sodium phosphate removed from the cupper a slurry with water, by the incorporation therewith of lime or colloidal clays. Other insecticides or fungicides may be incorporated with the normal copper phosphate or with the complex if desired. Our product being of extremely fine particle size and of low density is particularly useful when employed with the customary spreaders and adhesives Field experiments with our improved fungicide have indicated successful control .of the various fungus diseases which attack peach and apple trees, with considerably less damage to the plant than commercial Bordeaux mixture.

What we claim is:

1. The process for the electrolytic production of copper phosphate comprising subjecting an aqueous electrolyte containing sodium sulphate and sodium phosphate and substantialy free of chloride and chlorate ions, to the electrolytic action of a direct current in the presence of a copper anode and removing copper phosphate from the-electrolyzed solution.

2. The process for the electrolytic production of copper phospha/te comprising subjecting an equeous, substantially chlorine-free, electrolyte containing sodium .sulphate andv sodium phosphate, and having a pH within the range of 5.0 to 8.0, to-the electrolytic action of a direct current in the presence of a copper anode, and removing 'copper phosphate from theelectrolyte.

3. The process for the electrolytic production of copper phosphate comprising subjecting an aqueous electrolyte, substantially free of chloride and chlorate ions and containing sodium sulphate and sodium phosphate in dilute solutions, said solution having a pH within the range of 6.0 to 6.4 to the electrolytic action of a direct current in the presence of a copper anode and removing copof copper phosphate comprising subjecting an aqueous electrolyte substantially free of chloride and chlorate ions and containing sodium sulphate and sodium phosphate in dilute solution, said solution having a pH within the range of 5.0 to 8.0, to the electrolytic action of a direct current emperesper square foot of anode area, and removingcopper phosphate from the electrolyte.

5. The process for the preparation of copper phosphate comprising subjecting an aqueous electrolyte comprising a dilute solution of sodium sulphate and sodium phosphate, said electrolyte being substantially free of chloride and chlorate ions, to the electrolytic action of a direct current in the presence of a copper anode and maintainploying a copper anode in said electrolyte at a current density within the range of 15 to aming the pH of the electrolyte within the range of 5.0 to 8.0 by the addition of phosphoric acid and sodium phosphate to said electrolyte.

CHARLES F. BOOTH. HERBERT J. KRASE.