Patent GB-692063-A (GB)
Title: Improvements in or relating to manufacture of ferric dithiocarbamates
Filed: 1951-03-15
Abstract: A ferric salt of a di-aliphatic dithiocarbamic acid is made by adding to an aqueous solution of a water-soluble di-aliphatic dithiocarbamate an aqueous solution of a water-soluble ferric salt in an amount less than the chemically equivalent quantity required to combine with the total dithiocarbamic acid.  A convenient quantity of the iron salt precipitant is approximately 90-98 per cent of the chemically equivalent amount.  In examples: (1) the following precipitants in the form of 15 per cent aqueous solutions are added to 10 per cent by weight aqueous solutions of sodium dimethyl dithiocarbamate, (a) a chemically equivalent amount of ferric sulphate, (b) 10 per cent excess of the chemically equivalent amount of ferric sulphate, and (c) 96 per cent of the chemically equivalent amount of ferric sulphate; a table is given which shows that the resulting salt is free of oxidation potential only in the case of the latter precipitant; (2) a 22 per cent aqueous solution of Fe2(SO4)3 6.83 H2O is added to a 10 per cent aqueous solution of sodium dimethyl dithiocarbamate, the ferric salt formed being filtered off, washed and then dried at 55 DEG  C. for 18 hours; a sample of the dried salt shows no loss of weight after 168 hours in an air oven at 115 DEG  C., whereas when the salt is made from the chemically equivalent amount of ferric sulphate and tested for stability there is an appreciable loss of weight.  When the pure ferric salt is not required, e.g. in fungicidal applications (see Group VI), the residual dithiocarbamate remaining after the ferric dithiocarbamate precipitation may be precipitated by adding water-soluble salts of other heavy metals, e.g. zinc, copper, lead, mercury, or silver.  In an example of this modification an aqueous solution containing 95 per cent of the chemically equivalent amount of ferric sulphate is added to an aqueous solution of sodium dimethyl dithiocarbamate and sufficient of an aqueous solution of zinc sulphate is then added to precipitate the residual dithiocarbamate as zinc dimethyl dithiocarbamate; the combined zinc and ferric salt precipitate is then filtered off, washed and dried and tested for stability in an air circulating oven at 115 DEG  C.; similar results are obtained using zinc chloride, copper sulphate, lead nitrate or silver nitrate instead of the zinc sulphate.  Instead of ferric sulphate other water soluble ferric salts, e.g. ferric chloride may be used and instead of using sodium dialiphatic dithiocarbamates other water soluble dithiocarbamates, e.g. the potassium and ammonium salts may be used. Other dithiocarbamates which may be prepared by the process are ferric diethyl (or dibutyl-) dithiocarbamate and the ferric salts of N-2-cyanoethyl-N-methyl- (N-ethyl or N-butyl) dithiocarbamic acids.ALSO:A mixture of a ferric and other heavy metal salt of a di-aliphatic dithiocarbamic acid may be used in fungicidal applications the said mixture being obtained (see Group IV (b)) by adding to an aqueous solution of a water-soluble di-aliphatic dithiocarbamate an aqueous solution of a water-soluble ferric salt in an amount less than the chemically equivalent quantity required to combine with the total dithiocarbamic acid and then adding a water-soluble salt of another heavy metal, e.g. zinc, copper, lead, mercury, or silver, in amount sufficient to precipitate the remainder of the dithiocarbamic acid.  In an example the water soluble dithiocarbamate is sodium dimethyl dithiocarbamate, the water soluble ferric salt is ferric sulphate and the other heavy metal salt is zinc sulphate.  Instead of the latter zinc chloride, copper sulphate, lead nitrate and silver nitrate may be employed.  Reference is also made to the use of ferric chloride and to the use of potassium and ammonium di-aliphatic dithiocarbamates.