Propanal cyanohydrin

PROPANE CYANOHYDRIN (75-86-5) Combustible liquid (flash point 165°F/74°C). Reacts violently with strong oxidizers. Heat causes decomposition and formation of deadly cyanide gas. Contact with strong acid or strong bases may cause explosions. Slowly decomposes to acetone and hydrogen cyanide at room temperatures rate is accelerated by increase in heat, pH, or water content. Incompatible with ammonia, amines, cresol, organic anhydrides, alkylene oxides, epichlorohydrin, captrolactam solution, ammonia, isocyanates, phenols, reducing agents. 

To understand how steric factors affect the stability of the transition state leading to the final product. Let us consider the reactions of propanone and propanal with HCN to give cyanohydrin products ... 

Both propanone and propanal are planar molecules. The cyanohydrin products are tetrahedral. Thus, the reaction leads to a marked difference in shape between the starting carbonyl compound and the cyanohydrin product. There is also a marked difference in the space available to the substituents attached to the reaction site, i.e. the carbonyl carbon. The tetrahedral molecule is... 

Figure 20.5 Once-through and recycle processes for propane to acrylonitrile (ACH acetone cyanohydrins). Adapted from [18a].

A noteworthy example of an unexpected result in this area is the cyanation of l-chloro-3-phenyl-propan-2-one (15) with sodium or potassium cyanide in aqueous acetone which yielded the condensation product 16 in 55% yield.It is proposed that the reaction occurs via a Favorskii-type 1,3-dehydrochlorination, followed by trapping of the intermediate cyclopropanone 18 by cyanide to give cyanohydrin 19, which is not isolable. Instead, it adds across the intermediate cyclopropanone 18 to give adduct 20, which opens in the so-called normal way to afford the most stable carbanion 21, the benzylic carbanion. On protonation, the final cyclopropanecar-bonitrile 16 is formed and isolated as one stereoisomer, resulting from stereospecific addition of cyanide to the intermediate cyclopropanone. As expected, the isomeric 1-chloro-l-phenyl-propan-2-one (17) reacted in similar manner with aqueous cyanide to afford adduct 16, albeit in a lower yield. 

The current industrial production of methylmethacrylate by the acetone-cyanohydrin process suffers from a number of drawbacks, which make it environmentally unfriendly. In particular, it makes use of a very toxic reactant (HCN) and intermediate (acetone cyanohydrin), and coproduces large amounts of impure ammonium sulphate, contaminated with organic compounds. Among the several alternative synthetic routes which have been proposed, particularly interesting from both the practical and scientific points of view is the single-step oxidation of isobutane to methacrylic acid, intermediate in the synthesis of methylmethacrylate. Several industrial companies have studied this reaction (and the selective oxidation of propane to acrylic acid, as well), and it has been established that the most active and selective catalysts are those which are based on Keggin-type polyoxometalates (POM s), containing phosphorus and molybdenum as the main components [1-18]. 

Cyanohydrin silyl ethers Yttrium isopropoxide-more likely, the ((-PrO),3Y50 species—complexes with l,3-bis(2-methylferrocenyl)propane-l,3-dione (1) to afford a highly efficient catalyst for the asymmetric silylcyanation of electron-rich aromatic aldehydes with MCjSiCN. 

They form addition compounds with hydrogen cyanide to give cyanohydrins . For example, propanal gives 2-hydroxybutanonitrile ... 

The preparation of cyanohydrins is an important reaction in organic synthesis because it is used to lengthen the hydrocarbon chain by one C-atom the molecule of 1-cyanopropanol in the scheme above has one carbon atom more than the starting propanal. Some cyanohydrins are natural products, especially the derivatives of benzaldehyde, which are poisonous and used by particular insects for their defense. The toxic activity of these compounds is based on the hydrolysis of cyanohydrins into benzaldehyde and highly toxic HCN. 

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