Hydrogen cyanide yield

The hydrogen cyanide yields ammonia again in contact with heated water vapour —... 

The glycerol is converted into the symmetrical, or, i -3 -di-chlor-hydrine. By oxidation this yields the symmetrical, or, 1-3-di-chlor acetone, which by the addition of hydrogen cyanide yields the addition product, that on hydrolysis is converted into a hydroxy acid, viz., di-chlor hydroxy iso-butyric acid. By treatment with potassium cyanide this yields the corresponding di-cyanide, or nitrile of citric acid which on hydrolysis yields citric acid. 

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. 

Tertiary amines capable of eliminating a secondary amine to form a conjugated system can react with hydrogen cyanide to form y-keto nitriles by amine replacement. Thus (I) yields p-benzoylpropionitrile (IV) ... 

Cool the filtrate (A) to 5-10° and add concentrated hydrochloric acid dropwise and with vigorous stirring (FUME CUPBOARD hydrogen cyanide is evolved) to a pH of 1-2 (about 50 ml.) a crude, slightly pink 3-indoleacetic acid is precipitated. The yield of crude acid, m.p. 159-161°, is 20 g. Recrystallise from ethylene dichloride containing a small amount of ethanol 17 -5 g. of pure 3 indoleacetic acid, m.p. 167-168°, are obtained. 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

The maximum yield of 2-alkylseIenazole is 25%. In this way. 4-methylselenazole (7) was obtained starting from hydrogen cyanide, hydrogen selenide and chloroacetone. It is the only known selenazole not substituted in the 2-position. The yield relative to chloroacetone is very low (2.5%) (Scheme 2). 

The presence of an aldehyde function m their open chain forms makes aldoses reactive toward nucleophilic addition of hydrogen cyanide Addition yields a mixture of diastereo meric cyanohydrins... 

C20H27NO11, (3) is the most important of the cyanogenetic glycosides that yield hydrogen cyanide on hydrolysis. It is found in all seeds of the rose family... 

Yields based on propylene are 50—75%, and the main by-products are acetonitrile and hydrogen cyanide (96). 

Reaction of (58) with unsaturated nittile (59) produces 5-cyanopyrazoline (60), which on treatment with sodium ethoxide eliminates hydrogen cyanide to provide the pyrazole (61) in high yield (eq. 13). 

Chemical Synthesis. The first synthesis of ascorbic acid was reported ia 1933 by Reichsteia and co-workers (14,39—42) (Fig. 4). Similar, iadependent reports pubHshed by Haworth and co-workers followed shordy after this work (13,43—45). L-Xylose (16) was converted by way of its osazone (17) iato L-xylosone (18), which reacted with hydrogen cyanide forming L-xylonitfile (19). L-Xylonitfile cyclized under mild conditions to the cycloimine of L-ascorbic acid. Hydrolysis of the cycloimine yielded L-ascorbic acid. The yield for the conversion of L-xylosone to L-ascorbic acid was ca 40%. 

Racemic pantolactone is prepared easily by reacting isobutyraldehyde (15) with formaldehyde ia the presence of a base to yield the iatermediate hydroxyaldehyde (16). Hydrogen cyanide addition affords the hydroxy cyanohydria (17). Acid-cataly2ed hydrolysis and cyclization of the cyanohydria (17) gives (R,3)-pantolactone (18) ia 90% yield (18). 

Enantioselective addition of hydrogen cyanide to hydroxypivaldehyde (25), catalyzed by (lf)-oxynittilase, afforded (R)-cyanohydrin (26) in good optical yield. Acid-catalyzed hydrolysis followed by cyclization resulted in (R)-pantolactone in 98% ee and 95% yield after one recrystallization (56). 

Hydrogen cyanide adds to an olefinic double bond most readily when an adjacent activating group is present in the molecule, eg, carbonyl or cyano groups. In these cases, a Michael addition proceeds readily under basic catalysis, as with acrylonitrile (qv) to yield succinonitnle [110-61-2], C4H4N2, iu high yield (13). Formation of acrylonitrile by addition across the acetylenic bond can be accompHshed under catalytic conditions (see Acetylene-DERIVED chemicals). 

The Shawinigan process uses a unique reactor system (36,37). The heart of the process is the fluohmic furnace, a fluidized bed of carbon heated to 1350—1650°C by passing an electric current between carbon electrodes immersed in the bed. Feed gas is ammonia and a hydrocarbon, preferably propane. High yield and high concentration of hydrogen cyanide in the off gas are achieved. This process is presently practiced in Spain, AustraUa, and South Africa. 

In one patent (31), a filtered, heated mixture of air, methane, and ammonia ia a volume ratio of 5 1 1 was passed over a 90% platinum—10% rhodium gauze catalyst at 200 kPa (2 atm). The unreacted ammonia was absorbed from the off-gas ia a phosphate solution that was subsequently stripped and refined to 90% ammonia—10% water and recycled to the converter. The yield of hydrogen cyanide from ammonia was about 80%. On the basis of these data, the converter off-gas mol % composition can be estimated nitrogen, 49.9% water, 21.7% hydrogen, 13.5% hydrogen cyanide, 8.1% carbon monoxide, 3.7% carbon dioxide, 0.2% methane, 0.6% and ammonia, 2.3%. 

In the BMA process, methane (natural gas) and ammonia are reacted without air being present (44). The reaction is carried out in tubes that are heated externally to supply the endothermic heat of reaction very similar to a reformer. Yield from ammonia and methane is above 90%. The off-gas from the converter contains more than 20 mol % hydrogen cyanide, about 70 mol % hydrogen, 3 mol % ammonia, 1 mol % methane, and about 1 mol % nitrogen from ammonia decomposition. 

After removal of the unreacted ammonia and recovery of hydrogen cyanide, the waste gas is essentially all hydrogen suitable for other chemical use. The advantages of the BMA process are the high ammonia and natural gas yields and the usehil hydrogen waste gas, but the high investment and maintenance for the converter is a decided disadvantage. 

The fluohmic process is a third process for manufacturing hydrogen cyanide, which is being appHed in Spain and AustraUa. This process involves the reaction of ammonia with a hydrocarbon, usually propane or butane, in a fluidized bed of coke particles. The endothermic heat of reaction is suppHed electrically through electrodes immersed in the fluid bed. Yields from propane and ammonia are reportedly above 85% and the waste gas is essentially hydrogen, but the costs for electricity are high. Thus this process is appHcable only when there is an inexpensive source of power. 

Ammonium cyanide [12211-52-8] NH CN, a colorless crystalline soHd, is relatively unstable, and decomposes into ammonia and hydrogen cyanide at 36°C. Ammonium cyanide reacts with ketones (qv) to yield aminonitriles. Reaction of ammonium cyanide with glyoxal produces glycine. Because of its unstable nature, ammonium cyanide is not shipped or sold commercially. Unless it is kept cool and dry, decomposition releases vapors and forms black hydrogen cyanide polymer. 

High yields of optically active cyanohydrins have been prepared from hydrogen cyanide and carbonyl compounds using an enzyme as catalyst. Reduction of these optically active cyanohydrins with lithium aluminum hydride in ether affords the corresponding substituted, optically active ethanolamine (5) (see Alkanolamines). 

Formaldehyde Cyanohydrin. This cyanohydrin, also known as glycolonitrile [107-16-4], is a colorless Hquid with a cyanide odor. It is soluble in water, alcohol, and diethyl ether. Equimolar amounts of 37% formaldehyde and aqueous hydrogen cyanide mixed with a sodium hydroxide catalyst at 2°C for one hour give formaldehyde cyanohydrin in 79.5% yield (22). 

Single-pass conversions of acetone cyanohydrin are 90—95% depending on the residence times and temperatures in the generator and hold tank. Overall yields of product from acetone and hydrogen cyanide can be >97%. There are no significant by-products of the reaction other than the sodium salts produced by neutralization of the catalyst. 

Cyanohydrin Synthesis. Another synthetically useful enzyme that catalyzes carbon—carbon bond formation is oxynitnlase (EC 4.1.2.10). This enzyme catalyzes the addition of cyanides to various aldehydes that may come either in the form of hydrogen cyanide or acetone cyanohydrin (152—158) (Fig. 7). The reaction constitutes a convenient route for the preparation of a-hydroxy acids and P-amino alcohols. Acetone cyanohydrin [75-86-5] can also be used as the cyanide carrier, and is considered to be superior since it does not involve hazardous gaseous HCN and also virtually eliminates the spontaneous nonenzymatic reaction. (R)-oxynitrilase accepts aromatic (97a,b), straight- (97c,e), and branched-chain aUphatic aldehydes, converting them to (R)-cyanohydrins in very good yields and high enantiomeric purity (Table 10). 

The apphcation of (5)-oxynitrilase has been reported only recendy (159). The enzyme isolated from shoots of Sorghum catalyzes the condensation between various 3- and 4-substituted benzaldehydes and hydrogen cyanide resulting in (5)-cyanohydrins in 80—90% yield and up to 99% ee. 

With Hydrogen Cyanide. Ethylene oxide reacts readily with hydrogen cyanide ia the presence of alkaline catalysts, such as diethylamine, to give ethylene cyanohydria. This product is easily dehydrated to give acrylonitrile ia 80—90% yield ... 

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