3,230,260 United States Patent Office Patented Jan. 18, 1966 2 3,230,260 acid this does not occur. Thus the relatively non-volatile PROCESS FOR THE SOLATION OF N,O-DIMETH acid salts of N,O-dimethylhydroxylamine can be formed YLHYDROXYLAMINE Such as the hydrochloride, the sulfate or hydrogen sul Jack A. Snyder, Claymont, Del, assignor to E. I. du Pont fate. Sulfamic acid or phosphoric acid can similarly be de Nemours and Company, Wilmington, Del, a cor 5 used though they are less preferred. An amount of acid poration of Delaware can be used which is at least stoichiometrically equivalent No Drawing. Filed May 26, 1961, Ser. No. 112,772 to N.O-dimethylhydroxylamine and is preferred. Less 2 Claims. (C. 260-583) than stoichiometric amounts can be used though as less This invention relates to the preparation of N.O-di and less acid is used there will be loss of yield. While methylhydroxylamine. The invention is more particu O the processes of the invention can be operated with a pH larly directed to processes for the isolation of NO up to about 9, it is ordinarily preferred to use a pH dimethylhydroxylamine from a mixture of O-methylhy around 1 or 2. droxylamine and N,O-dimethylhydroxylamine by adding The amount of O-methylhydroxylamine and N.O-di formaldehyde thereby to convert O-methylhydroxylamine methylhydroxylamine dissolved in an aqueous solution to O-methylformaldoxime which escapes as a gas. 5 will ordinarily be of the order of 1 molar though it can By the methylation of hydroxyurethane followed by be higher or lower. The molarity of O-methylhydroxyl hydrolysis and distillation, one can make a mixture of amine and N.O-dimethylhydroxylamine combined can O-methylhydroxylamine and N.O - dimethylhydroxyla often run to 2 molar though there is no reason why it mine. The methylation produces additional materials as should not go up to 5 or 6 or even more. does the hydrolysis but these are separated out, for the 20 According to the invention formaldehyde is used to most part, in the distillation. Such a process is described effect a conversion of O-methylhydroxylamine to in Major and Fleck J.A.C.S. 50 1479 (1928). O-methylformaldoxime. The formaldehyde can be the A material produced as just described or a mixture of ordinary formalin solutions of commerce which contain O-methylhydroxylamine and N.O-dimethylhydroxylamine about 37% CHO and small amount of methanol. Other prepared in any fashion can be employed as a starting 25 forms of formaldehyde can equally well be used depend material in processes of the present invention. O-methyl ing upon the process equipment and one can for example hydroxylamine and N.O-dimethylhydroxylamine are ex use gaseous CH2O. Similarly, aqueous solutions of tremely difficult to separate by ordinary means because formaldehyde can be used which are produced by depo N,O - dimethylhydroxylamine boils at 42 C. and lymerization of paraformaldehyde by using a little caustic. O-methylhydroxylamine boils at 48 C. The difference 30 The techniques of supplying substantially monomeric of only 6 degrees makes separation by distillation vir formaldehyde for reaction are well understood. tually impossible and it is made even more difficult by The amount of formaldehyde to use is, of course, de the desired product being the lower boiling of the two. termined by the amount of O-methylhydroxylamine in a According to the present invention O-methylhydroxyl mixture to be treated. The formaldehyde reacts stoi amine and N.O-dimethylhydroxylamine are separated by 35 chiometrically with O-methylhydroxylamine and should the addition of formaldehyde, preferably in acid solution, be used in an amount to remove whatever proportion of to leave N.O-dimethylhydroxylamine substantially un O-methylhydroxylamine one wishes to take out of the changed and to produce O-methylformaldoxime which, mixture. Ordinarily it is desired to take out all in which being volatile, escapes as a gas. This reaction and case a slight excess of formaldehyde would ordinarily be procedure can be illustrated as follows: 40 employed. Even a large excess can be used because the I CH3ONE acid III CEON=CH formaldehyde is readily removed from the product Wutil CH2O --> the O-methylformaldoxime by distillation. II CHONECH3 I CEONHCH3 The reaction of formaldehyde can be conducted at In the above: room temperatures but can also be operated at higher 45 temperatures in which event the subsequent heating step I is O-methylhydroxylamine, which is preferred becomes a part of the formaldehyde II is N,O-dimethylhydroxylamine, and addition step and not a separate operation. III is O-methylformaldoxime. After O-methylformaldoxime has been formed or is In addition to O-methylhydroxylamine and N.O-di forming it is ordinarily desired to heat the aqueous solu methylhydroxylamine a commercial mixture often con 50 tion to reflux temperatures, that is to say temperatures tains other materials depending upon the process of pro near 100° C. O-methylformaldoxime which because of duction. Ordinarily such additional materials can be its volatility is already leaving the solution is driven off separated by conventional means either before or after more completely by the elevated temperature. Formal treatment according to the present invention. dehyde, too, is driven from the solution by the heating. The relative proportions of O-methylhydroxylamine 55 After O-methylformaldoxime and formaldehyde have and N,O-dimethylhydroxylamine can vary over a wide been driven from the solution it is cooled and the pH is range depending upon the completeness of the methyla raised by the addition of a suitable alkali such as sodium tion in the process by which they are produced or, more hydroxide. The pH should be above 4 and it is preferred broadly, depending upon the process by which they are that it be above 6. Ordinarily the pH will be above 7. produced. For purposes of the present invention it is 60 The exact pH is not at all critical. immaterial how much of O-methylhydroxylamine is The product, N.O-dimethylhydroxylamine, is then re present with N.O-dimethylhydroxylamine because any moved by distillation and it is to be observed that as the where from near traces up to quite substantial amounts product is removed the pH tends to fall and it should can be removed. be kept above 4 or preferably above 6 or 7 as above noted Processes of the invention are ordinarily conducted in 65 by further additions of alkali. Alternatively one can aqueous solutions and it is more desired that the solution use larger amounts of alkali initially. be at a pH below 7. The reason for having a low pH In order that the invention may be better understood is that if NO-dimethylhydroxylamine is present in the reference should be had to the following illustrative ex free state as an amine the escaping O-methylformald amples: oxime will tend to carry some of the N.O-dimethylhy 70 Example 1 droxylamine with it, thus leading to a loss in yield. If NO-dimethylhydroxylamine is combined with an A mixture of O-methylhydroxylamine hydrochloride 3,230,260 3 4. and N.O-dimethylhydroxylamine hydrochloride is pre heated to the reflux temperature and gaseous O-methyl pared as described by Major and Fleck except that the formaldoxime and excess formaldehyde are distilled over crude amine hydrochloride mixture is not recrystallized with about 200 ml, of water. The acidic solution is made after evaporation to remove alcohol and other volatiles. alkaline with 80 parts by weight of 50% aqueous NaOH, An aqueous solution of the mixed amine hydrochlorides and the freed amines are distilled. Two 100 ml. aqueous is prepared which has the following composition: amine fractions are taken. The first fraction proved to Percent contain all the amines. Analysis by gas chromatography O-methylhydroxylamine --------------------- 2.2 indicates the following recoveries of amines: N.O-dimethylhydroxylamine ------------------ 15.25 Parts by weight Hydroxylamine and other unidentified 10 O-methylhydroxylamine --------- Absent. basic impurities -------------------------- 1.3 N.O-dimethylhydroxylamine ------ 26.3 (0.43 mole). To 600 parts by weight of the above solution contain N,NO-trimethylhydroxylamine --- 1.2 (0.016 mole). ing 91.6 parts by weight (1.50 moles) of N.O-dimethyl Thus, the O-methylhydroxylamine has been completely hydroxylamine and 13.2 parts by weight (0.28 moles) of 15 eliminated from the solution while the desired N.O-di O-methylhydroxylamine at approximately pH 2.0 is added methylhydroxylamine is recovered substantially undimin 25.8 parts by weight (a 10% excess) of 36% aqueous ished. Instead of using sulfuric acid as in the above ex formaldehyde (9.3 parts by weight, 0.31 moles HCHO). ample there can be used molecularly equivalent amounts The resulting solution is heated slowly to reflux while of hydrochloric acid (Example 1), or phosphoric acid or gases from the top of the condenser operating at 10 C. 20 any other non-reactive acid of sufficient strength to fix the are led into a trap cooled by solid carbon dioxide and ace amine in substantially non-volatile condition during re tone. Gaseous O-methylformaldoxime is evolved from moval of excess formaldehyde. about 30° C. up to the reflux temperature. About 17 I claim: parts by weight of solid is collected in the trap (theoret 1. A process for isolating N.O-dimethylhydroxylamine ical: CHON=CH 16.5 parts by weight). The solid 25 from a mixture of O-methylhydroxylamine and N.O-di melted at about -65 C. and boiled at about -12 C. methylhydroxylamine by adding formaldehyde to an The corresponding constants for O-methylformaldoxime aqueous solution of O-methylhydroxylamine and N.O- are B.P.