US2720540A - Manufacture of sarcosine - Google Patents

Description

' the solution be clear.

MANUFACTURE OF SARCOSINE Waldo R. Caverly, Carneys Point, N. J assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application May 7, 1954, Serial No. 428,377

4 Claims. (Cl. 260-534) This invention relates to the manufacture of sarcosine. It is an object of this invention to provide a process for manufacturing this compound whereby the residual cyanide content of the product shall not exceed 5 parts per million. Various additional objects and achievements of this invention will become apparent as the description proceeds.

Sarcosine is N-methylamino-acetic acid, sometimes also referred to as N-methyl glycine. It is a water-soluble, crystalline solid, having several commercial uses, one being as an intermediate in the synthesis of anti-enzyme agents for tooth paste. Its manufacture on a commercial scale generally involves starting with an alkali-metal cyanide and formaldehyde, which are reacted together to form the corresponding salt of glycollic nitrile, thus:

MCN-l-HCHO MOCHzCN wherein M stands for sodium or potassium.

This salt is acidified to glycollic nitrile, which is then caused to react with monomethylamine as follows:

HOCHzCNd-CHaNHz-a CHaNHCHzCN-l-HzO The resulting methylaminoacetonitrile gives a salt of sarcosine on hydrolysis with strong alkali.

Usually the cyanide and alkali are sodium cyanide and sodium hydroxide, respectively. Because of the latter, the product is the sodium salt of N-methylglycine.

The above reactions are generally carried out in aqueous solution, and customarily reaction vessels made of iron or containing iron are employed.

When standardized as an aqueous solution, as is often done in commercial operations, it is highly desirable that To this end, iron contamination by reagents and rusty equipment and drums is kept as low as practicable. Ferric hydroxide is removed by filtration at some stages of the operation. As a safety precaution against an unnecessary health hazard in the acidification step, care is taken to assure almost complete reaction of the metal cyanide with formaldehyde before the acid is added.

In spite of these refinements in the process, the product quality sometimes is not as high as required for certain specific uses. It appears that the presence of iron somehow makes it more ditficult to completely consume the cyanide reactant or to eliminate its residual quantities from the reaction product. On the other hand, avoidance of iron equipment in the manufacture and packaging of the product is not always economically feasible.

Now I have found that the quantity of residual cyanides in sarcosine, manufactured by the above process in iron equipment, can be minimized if the entire series of reactions is carried out in the presence of a water-soluble oxidizing agent, such as an alkali-metal or alkaline-earth hypochlorite, hydrogen peroxide, or an alkali-metal nitrite, peroxide, or perborate.

The quantity of oxidizing agent required is not great. It suffices to create and maintain in the reaction mass, throughout the synthesis, a quantity of available oxygen ice equal to about 0.25 part by weight for each 100 parts by weight of the metal cyanide employed. Another way of defining essentially the same thing is to state that the reaction mass shall give a clear, positive test to starchiodide paper at all times.

To achieve the above, the oxidizing agent is preferably added portionwise, as may be needed according to the starch-iodide test. A convenient procedure is to add one portion of the oxidizing agent to the water in which the metal cyanide is to be dissolved, and another portion to the solution of the glycollic nitrile salt formed in the first step of the reaction, just prior to acidification.

The oxidizing agent may be added in the form in which it is obtained on the market-i. e., in solid form or as a solution in water.

The action of the oxidizing agent is not clearly understood. It is conceivable that the oxidizing agent acts to keep the iron impurities in ferric state, in which form apparently they have no strong tendency to form iron cyanide complexes, or form complexes which are broken up readily during the alkaline hydrolysis of the nitrile. But whatever the theory, it is clear that my invention achieves an unforeseen but very useful effect. It is to be understood thereforethat I do not wish to limit my in- Example 1 Into an iron pot containing 900 parts of water, 2.0 parts of 52% aqueous sodium hypochlorite were added,

and followed by 3 parts of 30% caustic soda and 98 parts The solution was cooled to 51'0 C. and 168 parts of iron-free, 37%,. formaldehyde of 96% sodium cyanide.

solution in water were added. The reaction mixture was maintained at 5l0 C. until the free cyanide content dropped to below 0.20%, as determined by the standard silver nitrate test. Then 2030 parts more of a 5.2% aqueous sodium hypochlorite solution was added.

Maintaining the temperature at 5-10" 0, the pH of the solution. was adjusted to 7.5 to 8.0. 220 parts of 30% hydrochloric acid (aqueous solution) were introduced into the solution, and the acidified nitrile mass was added to 157 parts of methylamine (40% aqueous solution) and 10 parts of 5.2% aqueous sodium hypochlorite at 5-10 C. The temperature was raised slowly to 20 C., and 300 parts of 30% aqueous caustic soda were stirred in. By raising the temperature to boiling, excess methylamine and ammonia were distilled off with some of the water, and the charge was concentrated to about 1000 parts. To this were added 2.5 parts of Nuchar (an activated carbon), and after some agitation, the mass was filtered.

The filtrate contained 0.8 p. p. m. cyanide, as compared to 300-1000 p. p. in. when the sodium hypochlorite was omitted.

Example 2 An iron pot was charged with 900 parts of water and 0.3 part of sodium nitrite crystals and then with 3 parts of 30% aqueous caustic soda and 98 parts of 96% so dium cyanide. The solution was cooled to 5l0 C., and 168 parts of iron-free, 37%, aqueous formaldehyde were added slowly enough to avoid heating above 510 C. After holding at 5l0 C. until the free cyanide content was below 0.20%, 5 parts of sodium nitrite crystals were added, followed by 220 parts of 30% hydrochloric acid. Finally, 30% hydrochloric acid solution was added to adjust the pH of the solution to 7.5 to 8.0. 157 parts of methylamine, as a 40% aqueous solution cooled to 0l0 C., were then added rapidly.

The temperature was raised slowly to 20 C. and held for" onehour; 300" parts of"3'0% aqueous caustic soda were added. The temperaturerwas then raised to boiling, to drive oif. excess methylamine, ammonia and water, and thesolution was vconcentrated to: about 1000 parts, After adding 2.5"p'arts ofdecolorizing charcoal and agitating, theimass' was filtered; The filtrate contained 03' p. cyanide.

Example 3' In several other'experiments, following the, general procedure of Example 1, each of theafollowing wastested,

in=,equal1amounts, inlieuof sodium hypochlorite: calcium hypochlorite, potassium nitrite, sodium peroxide,v

hydrogen peroxide. and sodium perborate, In: a1l in.- stances, aqueous .solutions. of the sodium saltofsarcosine were obtained, containing, only, 0.5; to,- 5 p. p. n1. cyanide (based ,onweighti of; 1 33% solution).

Example 4 When. the, procedure ofJExamplel, was run with rusty tacks-in thereaction mixture, the cyanide content of the productwas only 0.69 p. p. m. In the absence of sodium hypochlorite, thecyanide content varied between300 and 1000 p. p. m.,apparently depending on the degreeof iron contamination.

It Willbe understood thatthe details of the aboveprogive in the reaction mass a positive test with starch-iodide test paper.

2. A process for producing a salt of sarcosine having a cyanide content not exceeding 5 parts per million by weight, which comprises forming a solution of an alkalimetal cyanide in water containing sodium hypochlorite in quantity corresponding to not less than 0.25 part by weight of ayailableoxygen foreach l00 p a rts of alkalimetal cyanide in solution, reacting said solution with aqueous formaldehyde until the concentration of. residual cyanide in solution dropsto below 0.20%, acidifyingfihe mass and reacting the same with an aqueous solution of methylamine; containing sodium hypochlorite, then alkalizing the mass, heatingtoexpel volatile matter and recovering the aqueous. solutionof thereaction product.

3. A process as in claim 2, the process including further addition of sodium hypochlorite when and as needed, to maintain in the reaction mass a sufiicient concentration, of availableoxygen to give a positive starch-iodide test;

4; A process for producing a'salt of sarcosinehaving acyanide content not exceeding 5 parts" per million by weight; which comprises forming a solution of an alkalirnetal cyanide in water'containing sodium nitrite in quantity corresponding to not less than 0.25 part by weight of tity ofaqueous sodium nitrite, acidifying, and reacting. the mass with an aqueous solution of methylamine, then alkalizing the mass, heatingto expelvolatilematter, and

recoveringthe aqueoussolution of the reaction product.

References Cited in the file of this patent UNITED STATES PATENTS 2,175,805 Iacobson Oct. 10, 1939.

Claims (1)

1. IN THE PROCESS OF PREPARING SARCOSINE BY REACTION OF AN ALKALI-METAL CYANIDE WITH FORMALDEHYDE FOLLOWED BY REACTION WITH METHYLAMINE AND HYDROLYSIS OF THE NITRILE, THE IMPROVEMENT WHICH CONSISTS OF CARRYING OUT ALL STEPS IN THE PRESENCE OF AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF THE ALKALI-METAL AND ALKALINE-EARTH HYPCHLORITES, ALKALI-METAL NITRITES, ALKALI-METAL PEROXIDES, ALKALI-METAL PERBORATES AND HYDROGEN PEROXIDE, THE CONCENTRATION OF OXIDIZING AGENT BEING AT LEAST ENOUGH TO GIVE IN THE REACTION MASS A POSITIVE TEST WITH STARCH-IODIDE TEST PAPER.