Methyl halides, oxidative carboxylation

Olah and Bukala404 have developed a method for the oxidative carboxylation of methyl halides with CO and copper oxides or Cu and oxygen over SbF5-graphite [Eq. (5.156)]. Time-dependence studies indicated that the three products—methyl acetate, dimethyl ether, and methyl fluoride—were formed in parallel reactions. The reactivity of methyl halides shows the decreasing order MeBr > MeCl > MeF. 

Sodium hypochlorite is used for the epoxidation of double bonds [659, 691] for the oxidation of primary alcohols to aldehydes [692], of secondary alcohols to ketones [693], and of primary amines to carbonyl compounds [692] for the conversion of benzylic halides into acids or ketones [690] for the oxidation of aromatic rings to quinones [694] and of sulfides to sulfones [695] and, especially, for the degradation of methyl ketones to carboxylic acids with one less carbon atom [655, 696, 697, 695, 699] and of a-amino acids to aldehydes with one less carbon [700]. Sodium hypochlorite is also used for the reoxidation of low-valence ruthenium compounds to ruthenium tetroxide in oxidations by ruthenium trichloride [701]. 

The oxidation of primary alkyl halides to carboxylic acids is accomplished on incubation of long-chain aliphatic fluorides, chlorides, bromides, and iodides with the yeast Torulopsis gropengiesseri [1086,1087] (equation 200). The biooxidation starts at the terminal methyl groups and gives w-halogenoalkanoic acids, which are ultimately converted to a,oj-dicarboxylic... 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Isomerism.—Isomerism in the case of the acids is of the same character as that of the alkyl halides and the alcohols if we consider the acids as mono-carboxyl substitution products of the hydrocarbons. In the five carbon acids, the pentanoic or valeric acids, we have one compound which possesses an asymmetric carbon atom. It is the 2-methyl butanoic-i acid. According to the van t Hofif-LeBel theory this compound should exist in three forms, dextro lew and inactive. By oxidation of the fermentation amyl alcohol which is a mixture of 2-methyl butanol-1 and 2-methyl butanol-4 there is obtained a mixture of two of the valeric acids, viz., the 2-methyl butanoic-i acid and the 2-methyl butanoic-4. This same mixture is found naturally in the roots of Valeriana officinalis. By separating out the 2-methyl butanoic-4 acid the 2-methyl butanoic-1 acid is obtained. This acid is inactive, but has nevery with certaintyy been separated into its optical components, though it is claimed that a dextro form has been obtained. 

Other nucleophilic carbon reagents, such as acetylide ions, and ions derived from ot-methylpyridines have also been used. A particularly useful nucleophile is the methylsulfinyl carbanion, CH3SOCH2-, ° the conjugate base of DMSO, since the p-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 624). The methylsulfonyl carbanion (CH3SO2CH2), the conjugate base of dimethyl sulfone, behaves similarly, ° " and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF will acylate l,3-dithianes ° (see 10-71) to give, after oxidative hydrolysis with NBS or NCS, a-keto aldehydes or... 

Oxidations with chromic oxide encompass hydroxylation of methylene [544] and methine [544, 545, 546] groups conversion of methyl groups into formyl groups [539, 547, 548, 549] or carboxylic groups [550, 55i] and of methylene groups into carbonyls [275, 552, 553, 554, 555] oxidation of aromatic hydrocarbons [556, 557, 555] and phenols [559] to quinones, of primary halides to aldehydes [540], and of secondary halides to ketones [560, 561] epoxidation of alkenes [562, 563,564, and oxidation of alkenes to ketones [565, 566] and to carboxylic acids [567, 565, 569]. 

Terminal methyl groups, as well as the halomethyl groups in aliphatic halides with 15-18 carbon atoms, are oxidized biochemically to carboxyls (equation 49) [1086, 1087],... 

Acid anhydrides as activated derivatives of carboxylic acids have found little attention for the preparation of acid halides. Their use can be justified if they are obtained from other sources than from carboxylic acids, e.g. phthalic anhydride from the oxidation of naphthalene or o-xylene. It is, therefore, no surprise that there exist patents to convert phthalic anhydride to phthalic acid dichloride with carbonyl dichloride in the presence of catalysts. " However, there are some methods available thus a,a-di-chloromethyl methyl ether will convert acid anhydrides to acid chlorides and brenzcatechyl phosphorus tribromide will also achieve this transformation. Fluorides may be prepared similarly with the pyridine/HF mixture of 01ah. °... 

The carbonylation of chloroarenes has been described by Alper and Grushin [27] and Jenner and Bentaleb [28], While the former showed that square-planar complexes of divalent palladium, [ L2PdCl2], where L = tertiary phosphine, are active catalysts for the biphasic carbonylation of aromatic halides, including chloroarenes (when L = tricyclohexylphosphine), to the corresponding carboxylic acids, the latter demonstrated that chloroarenes can be converted into aromatic acids via catalytic reaction with aqueous methyl formate under biphasic conditions. [ PdCl2(PCy3)2] was the most efficient catalyst. The addition of [ Ru3(CO)12] and ammonium formate improved yield and selectivity of the carbonylation reaction. The mechanism should involve oxidative addition of the C—Cl bond to a zero-valent Pd species followed by CO insertion. However, the palladium catalyst may also directly activate methyl formate. Compared to other carbonylations of aryl-Hal compounds the procedure is quite convenient (no solvent, no initial pressurization) [27]. 

Ethyne may be condensed first with the alkyl halide to give H3C [CH2]a C=CH or with the difunctional entity to give Hcic(CH2)yY. The carboxyl group can be generated by oxidation of an alcohol or by reaction of halide with cyanide and then with acidic methanol to give a methyl ester. Condensation with acetylene or an ethynyl compound requires the sodium or lithium derivative and is usually conducted in liquid ammonia. Modification of this approach is necessary when the unsaturated centre is close to either end of the molecule. 

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