2- Methylbutan dehydration

There is a strong similarity between the mechanism shown m Eigure 5 12 and the one shown for alcohol dehydration m Eigure 5 6 The mam difference between the dehy dration of 2 methyl 2 butanol and the dehydrohalogenation of 2 bromo 2 methylbutane IS the source of the carbocation When the alcohol is the substrate it is the correspond mg alkyloxonmm ion that dissociates to form the carbocation The alkyl halide ionizes directly to the carbocation... 

The reaction of a-bromoacetals with trimethylsilylenolates catalyzed by titanium tetrachloride provides /3-alkoxy-y-bromoketones, which are useful furan precursors (Scheme 33) (75CL527). A new synthesis of acylfurans is exemplified by the formation of the 3-acetyl derivative (146) by heating the brdmoalkene (145) (78JOC4596). 2,2-Dimethyl-3(2//)-furanone (148) has been synthesized from 3-hydroxy-3-methylbutan-2-one treatment with sodium hydride and ethyl formate gave the hydroxymethylene derivative (147), which was cyclized and dehydrated to the furanone (148) with hydrochloric acid (Scheme 34) (71TL4891). O... 

In the preparative example of the dehydration of 2-methylbutan-2-ol [Me2C(OH)-CH2-Me], the loss of a proton from the intermediate carbocation (2) may take place from either of the two adjacent positions giving a mixture of regioisomers, 2-methylbut-2-ene (3) and 2-methylbut-l-ene (1) (Expt 5.12). 

Isoprene epoxidized on the vinyl group (l,2-epoxy-3-methyl-3-butene, 14) would also be an attractive synthon for monoterpenoids if it were more readily accessible. Among the possible preparative methods (Scheme 2), acid-catalyzed isomerization of 2,3-epoxy-l-halo-3-methylbutanes (epoxidized prenyl halides) and dehydrohalogenation of the resulting isomers seemed the best route until chlorination of prenyl acetate (15, R = OAc) with hypochlorous acid was published. Dehydration of the mixture of products gave a maximum of the chloroacetate 16, which yielded the epoxide 14 with sodium hydroxide in methanol. ... 

Precipitation via Extended Chemicai Reaction. This can, perhaps, be considered as a subset of the previously described coprecipitation methodology however, in this case, a number of solution or surface processes occur prior to the formation of the final catalyst. In addition, coprecipitation involves the reaction between an acid and a base, but, in many cases, a catalyst precursor can be formed in the absence of a base. This is particularly the case for the formation of phosphates (eg, AIPO4, BPO4, and VPO catalysts). Typically, a metal salt is reacted with a phosphorus compound, typically phosphoric acid, under controlled conditions. The choice of the metal salt can influence the catalyst precursor structure. For example, for AIPO4, a catalyst for the formation of isoprene from the dehydration of 2-methylbutanal, the reaction of aluminium chloride with phosphoric acid gives a mixture of cristobalite and tridymite phases of AIPO4, whereas... 

Our belief that carbocations are intermediates in the addition of hydrogen halides to alkenes is strengthened by the fact that rearrangements of the kind seen in alcohol dehydrations (Section 5.13) sometimes occur. For example, the reaction of hydrogen chloride with 3-methyl-1-butene is expected to produce 2-chloro-3-methylbutane. Instead, a mixture of 2-chloro-3-methylbutane and 2-chloro-2-methylbutane results. 

Raw or gently pasteurised milk (e.g. for 10 seconds at 73 °C) has a fine characteristic odour and sweet taste. Typical components present in low concentrations are dimethylsulfide, biacetyl, 2-methylbutan-l-ol, (Z)-hept-4-enal and ( )-non-2-enal. Milk pasteurised at higher temperatures and Ultra High Temperature (UHT) milk present the so-called cooked flavour, the appearance of which is the first measurable manifestation of the chemical changes that occur in heated milk. The substances responsible for the cooked off-flavour are sulfane and other sulfur compounds. Of particular importance are dimethylsulfide, dimethyldisulfide and dimethyltrisullide that are produced from proteins contained in the membranes of fat particles and from thiamine. Also relevant are alkane-2-ones (methylketones) generated by thermal decarboxylation of P-oxocarboxylic acids (mainly hexane-2-one, heptane-2-one and nonane-2-one), y-lactones and 5-lactones produced by dehydration of y- and 5-hydroxycarboxylic acids (mainly 8-decalactone and y- and 8-dodecalactones). Important carbonyl compounds include biacetyl, hexanal, 3-methylbutanal, (Z)-hept-4-enal and ( )-non-2-enal. In the more intensive thermal treatment of milk (sterilisation), products of the Maillard reaction play a role, such as maltol and isomaltol, 5-hydroxymethylfuran-2-carbaldehyde, 4-hydroxy-2,5-dimethyl-2 f-furan-3-one (furaneol) and 2,5-dimethylpyrazine. 

The formation of the characteristic aroma of cocoa depends on a number of factors, such as good harvest, fermentation, drying and roasting of cocoa beans. Precursors of aromatic compounds are produced mainly by anaerobic fermentation of cocoa beans. The aroma of roasted beans is created largely by the Maillard reaction and caramehsation, and is represented by more than 400 compounds. The major components are aldehydes, sulfides, heterocyclic compounds, carboxylic acids and terpenoids. Important aldehydes are 2-methylpropanal and 2-methylbutanal, which recalls the smell of cocoa and malt, and ( )-2-phenyl-5-methylhex-2-enal (8-201), which resembles chocolate. The latter aldehyde is formed by aldol condensation of another important aroma component, 3-methylbutanal with phenylacetaldehyde, and dehydration of the aldolisation product. Linalool and 2-phenylethanol... 

Now let s draw the forward scheme. The 3° alcohol is converted to 2-methylpropene using strong acid. Anti-Markovnikov addition of HBr (with peroxides) produces l-bromo-2-methylpropane. Subsequent reaction with sodium acetylide (produced from the 1° alcohol by dehydration, bromination and double elimation/deprotonation as shown) produces 4-methyl-1-pentyne. Deprotonation with sodium amide followed by reaction with 1-bromopentane (made from the 2° alcohol by tosylation, elimination and anfi -Markovnikov addition) yields 2-methyl-4-decyne. Reduction using sodium in liquid ammonia produces the E alkene. Ozonolysis followed by treatment with dimethylsulfide produces an equimolar ratio of the two products, 3-methylbutanal and hexanal. 

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