Methacrylamide sulfate

Acetone cyanohydrin is used for methacrylate manufacture. Sulfuric acid is added in greater than an equimolar amount, and by thermal cracking the acetone cyanohydrin is converted to methacrylamide sulfate [29194-31-8]. 

One of the most important appHcations of this process is that of methyl methacrylate manufacture. In this process (81), acetone cyanohydrin is treated with sulfuric acid at 100°C, affording the corresponding methacrylamide sulfate which is esterified with methanol. After purification, methyl methacrylate (99.8% purity) is obtained in a yield of ca 85%. 

Inhibitors are introduced al specific points in the process to prevent polymerization Sulfuric acid serves as catalyst in a combined hydrolysis-esterilieaiion of methacrylamide sulfate to a mixture of methyl methacrylate and methacrylic acid. Conversion of methacrylamide sulfate to methyl methacrylate can be carried out using a variety of procedures for die recovery of crude methyl methacrylate and fur separation of methanol and methacrylic acid for recycling. A schematic of the overall process is given in Figure I. The overall yield based on acetone cyanohydrin is approximately 90D Most of Ihe world supply of MMA is still produced by this process. 

Fig. I MMA from acetone c umih>drin ia methacrylamide sulfate...

Methyl methacrylate (melting point -48°C, boiling point 100°C, density 0.9394, flash point 9°C) is produced by the acetone cyanohydrin process in which the acetone cyanohydrin (from the reaction of acetone with hydrogen cyanide, q.v.) is reacted with sulfuric acid to yield methacrylamide sulfate, which is further hydrolyzed and esterified. The process is continuous. 

This heating converts the intermediate compounds into methacrylamide sulfate. Longer periods of heating decrease the yield. 

The traditional acetone cyanohydrin (ACH) process is the most widely used in Europe and North America, while other processes are more often used in Asia. In the ACH process (Figure 2.63), acetone and hydrogen cyanide react to yield acetone cyanohydrin the latter is then reacted with an excess of concentrated sulfuric add to form methacrylamide sulfate. In a later stage, methacrylamide is treated with excess aqueous methanol the amide is hydrolyzed and esterified, with formation of a mixture of methyl methacrylate and methacrylic acid. The ACH process offers economical advantages, especially in Europe, where large plants are in use - most of them have been in operation for decades. The process also suffers from drawbacks that have been the driving forces for the development of alternative technologies. 

The process flowsheet is given in Figure 4.4 [38]. Acetone and hydrogen cyanide are reacted in a strong base. Sulfuric acid is used to neutralize excess alkali to prevent the decomposition of the cyanohydrin then sodium sulfate is filtered out and the unreacted HCN and acetone are recycled by distillation. The cyanohydrin is hydrolyzed with sulfuric acid to form methacrylamide sulfate. The methacrylamide sulfate reacts with methanol to form methyl methacrylate and ammonium bisulfate. Distillation removes methyl methacrylate and unreacted methanol which is recycled. Water extraction is used to remove any excess methanol and the monomer is purified to 99.8% in a rerun tower. This is the only process used in United States to produce methyl methacrylate [39]. 

This represents a two-step hydrolysis. In the first phase, it requires anhydrous reactants to avoid the formation of a-hydroxylamide, which is more difficult to convert to methacrylamide sulfate. It takes place in liquid medium, at atmospheric pressme, first at about 80 to 110°C, and then 125 to 145°C to complete the transformation, nidi residence tones of about 1 h, an HjSO /acetone cyanohydrin molar ratio of 1.5 to 2, and a molar yield of 95 to 97 per cent The main by-products are carbon monoxide and acetone disulfonic acid. It is necessary to operate in the presence of an inhibitor (phenol, phenothiazme, sulfur, etc.) to prevent the formation of polymers. 

Esters of methacrylic acid are obtained directly from acetone cyanohydrin by reaction of the latter with concentrated sulfuric acid to give methacrylamide sulfate, followed by reaction with an alcohol. The process is continuous and the methacrylamide sulfate is not isolated. Acetone cyanohydrin is derived from acetone and hydrogen cyanide (Pig. 15-39), Polymerization Procedures. Of particular importmice to the acrylics is the cast or bulk method of polymerization. This method is employed to produce cast polymethyl methacrylate sheets which are widely used in industrial applications. Careful control of polymerization is required to obtain a bubble-free product with good optical clarity. A typical flow sheet for the production of cast eet is shown in fig. lfi-40. Solution, suspension, and particularly emulsion polymerizations are also, widely used with the acrylics. Such polymerization reactions involve relatively conventional batch-type processes. i... 

Metal reaction vessel, 83, 102 Methacrylamide, 29, 61 Methacrylamide sulfate, 39, 62 Methacrylic acid, 29, 4 /3-Methallyl lactate, 26, 6 Methane, chlorotriphenyl-, 23,100, 102... 

Synthesis of methyl methacrylate is fundamental to the production of the transparent plastic polymethyl methacrylate (PMMA), and is estimated at over two million metric tons per year. The monomer is most commonly synthesized via the well-established Acetone Cyanohydrin (ACN) process, as shown below, based on easily available raw materials such as, acetone, hydrogen cyanide, methanol and sulfuric acid. Reaction of acetone and hydrogen cyanide yields acetone cyanohydrin as an intermediate, which is then reacted with excess amount of concentrated sulfuric acid, followed by thermal cracking to form methacrylamide sulfate. The methacrylamide sulfate intermediate is then further hydrolyzed and esterified with aqueous methanol to form methyl methacrylate. 

Commercial production [462] of methacrylates began in 1933 from acetone cyanhydrine, and this is still the basis for essentially all current commercial methacrylate production. The basic materials - acetone, hydrogen eyanide, and sulfuric acid - are available. In the first step, which needs anhydrous materials and conditions, methacrylamide sulfate is formed. The presence of water would form a-hydroxyisobutyramide as the main product. In the second step, methacrylamide sulfate is hydrolyzed by an excess of water to give methacrylic acid. 

Methacrylic acid can also be produced by a variety of processes including oxidation of ethylene, propylene, and isobutylene. The most common commercial process for making methacrylic acid is the acetone cyanohydrin (ACN) process. The feedstocks for this process are acetone, hydrogen cyanide, and sulfuric acid. The acetone and HCN are reacted under alkaline conditions to produce the cyanohydrin. Reaction of the cyanohydrin with sulfuric acid ultimately produces methacrylamide sulfate, hydrolysis of which produces methacrylic acid. Methyl methacrylate can be made either by esterifying the acid or directly by reacting the amide sulfate with methanol. 

---