Pyrolysis secondary alcohols

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Berti explored use of the reagent for the conversion of secondary alcohols into olefins by reaction of the alcohol with methyl chlorosulflte in ether containing pyridine to produce the methyl alkyl sulfites and pyrolysis of these esters, but the results were not impressive. 

It is generally accepted that degradation of epoxy resins starts by dehydration of secondary alcoholic groups followed by homolytic scission of the formed allylic bond [34, 35]. There have been various studies carried out for the brominated epoxy resin treatment. In the study of Balabanovich [33], brominated epoxy resin produces gases and oil as pyrolysis products at the temperature of about 100 °C. However, these pyrolysis volatiles are contaminated by brominated phenols, brominated alkanes, and HBr, which is a difficult point for pyrolysis of brominated epoxy resin. 

The total yield of 201 was increased and the synthesis time reduced by extracting [nC]butyric acid from its lithium salt by dry 0.1% HCl/He gas mixture and carrying out its pyrolysis at 530 °C over glass beads (equation 104). The relative reactivity of 201 to primary, secondary and tertiary alcohols (equation 105a, b, c) has been found to be as 1 0.4 0.1, respectively. Several bioactive compounds have been labelled with [nC]propyl ketene, such as carbohydrate compounds193 and IV-butyl compounds, for instance /V- 11 C]butyryl THPO, 202, and some phorbol esters192, 203, 204 and 205. 

Thermal decomposition of methyl xanthates is similar to the pyrolysis of acetates for the formation of the double bond. Olefins are obtained from primary, secondary, and tertiary alcohols without extensive isomerization or structural rearrangement. The other products of the pyrolysis of the methyl xanthates are methyl mercaptan and carbon oxy-sulfide. The xanthates prepared from primary alcohols are more difficult to decompose than those prepared from secondary and tertiary alcohols. Over-all yields of 22-51% have been obtained for a number of tertiary alkyl derivatives of ethylene. Originally the xanthates were made by successive treatment of the alcohol with sodium or potassium, carbon disulfide, and methyl iodide. In a modification of this procedure sodium... 

Boric acid is a mild dehydrating agent suitable for removal of water from some primary, secondary, or tertiary alcohols. Since the acid and the alcohol form first a trimeric metaboric ester, which then regenerates the boric acid when it decomposes to the olefin,36 the reaction is somewhat similar to pyrolysis of carboxylic esters but the boric acid dehydration occurs at appreciably lower temperatures (250-300°). Olefins are readily obtained by heating approximately molar equivalents of boric acid and 1-octanol, 1-heptanol, 1-hexanol, (—)-menthol, cyclohexanol, or 5cyclohexane-methanol, and cyclobutanemethanol.38... 

Since the pyrolysis was carried out under a dynamic vacuum, the organic products formed were removed quickly thus preventing secondary reactions. In control experiments, the product alcohols were passed over the residual Ti02 under pyrolytic conditions. With the exception of neopentyl alcohol, no significant dehydration was observed. Thus, our study differs from that reported by earlier by Bradley [3d]. Since the latter was done under a static vacuum, the alcohol formed underwent dehydration to generate water which, in turn, caused hyrolysis of the M-OR bonds. As a result, an autocatalytic decomposition of the metal alkoxide ensued. 

A further feature of the pyrolysis that emerges upon examination of the product distribution is that, with the exception of 7, the ratio of alcohol to ether formed increased markedly on going from primary (4 and 8) to secondary (5) to tertiary (6) alkoxide i.e., with increasing steric crowding at the a-carbon. This observation is most easily explained by a mechanism encompassing eqs. 3 and 4. 

Generally, the production of alkyl polyglycosides based on short-chain alcohols (Cg jg-OH) and with a low DP (large alcohol excess) presents the fewest problems. Fewer secondary products are formed with the increasing excess of alcohol in the reaction stage. The thermal stress and formation of pyrolysis products during ranoval of the excess alcohol are reduced. 

Addition of sodium derivatives of allyl alcohols to phenylthioacetylene furnishes adducts which on oxidation and pyrolysis undergo Claisen rearrangement and elimination of benzenesulphenic acid to yield 2,4-dienals Scheme 35). Similarly, primary and secondary allyl alcohols add to allenyl phenyl... 

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