Methyl halides, addition

Another method of replacing hydrogen by methyl, in addition to the use of alkyl halide and alkyl sulphate, is by the action of dIazomethane on the phenol... 

Methanol is an ideal starting material for the synthesis of many chemicals. It is the most important feedstock for the large-scale commercial production of acetic acid and formaldehyde. Additionally, a variety of other chemicals such as methyl esters, methyl halides and methyl ethers can be produced from it. Tenessee-Eastman s recent pioneering commercialization of a coal-based process for acetic anhydride production illustrates the growing importance of methanol as chemical feedstock. 

Conventional uses of methanol account for 90% of present consumption and include formaldehyde, dimethyl terephthalate, methyl methacrylate, methyl halides, methylamines and various solvent and other applications. Newer uses for methanol that have revitalized its growth and outlook include a new technology for acetic acid, single cell protein, methyl tertiary butyl ether-(MTBE), and water denitrification. Potential uses for methanol include its use as a carrier for coal in pipelines, as a source of hydrogen or synthesis gas used in direct reduction of iron ore, as a direct additive to or a feedstock for gasoline, peak power shaving and other fuel related possibilities. Table II lists the world methanol demand by end use in 1979. 

Cellulose Ethers. Cellulose ethers are formed when cellulose, in the presence of alkali or as alkali cellulose, is treated with alkyl or arylalkyl halides. Two types of reaction are employed in the preparation of cellulose ethers. The most common is nucleophilic substitution. Methylation of alkali cellulose with a methyl halide is an example of this type. The other type of etherification reaction is Michael addition. This reaction proceeds by way of an alkali-catalyzed addition of an activated vinyl group to the cellulose. The reaction of acrylonitrile with alkali cellulose is a typical example. The general reaction is outlined in Scheme 4. 

Cesium-exchanged zeolite X was used as a solid base catalyst in the Knoevenagel condensation of benzaldehyde or benzyl acetone with ethyl cyanoacetate [121]. The latter reaction is a key step in the synthesis of the fragrance molecule, citronitrile (see Fig. 2.37). However, reactivities were substantially lower than those observed with the more strongly basic hydrotalcite (see earlier). Similarly, Na-Y and Na-Beta catalyzed a variety of Michael additions [122] and K-Y and Cs-X were effective catalysts for the methylation of aniline and phenylaceto-nitrile with dimethyl carbonate or methanol, respectively (Fig. 2.37) [123]. These procedures constitute interesting green alternatives to classical alkylations using methyl halides or dimethyl sulfate in the presence of stoichiometric quantities of conventional bases such as caustic soda. 

Linnett o gives a discussion of the use of valence force fieid with the addition ol selected cross terms. One method of reducing the number of constants to Tdc determined from the frequencies is to carry over from molecule to molecule certain force constants for squared terms and even for cross terms. Linnett mentions in this connection the work of Crawford and Brinkley who studied acetylene, ethane, methylacetylene, dimethylacetylene, hydrogen cyanide, methyl cyanide and the methyl halides in this way, and were able, for all the molecules, to account for 84 frequencies with 31 constants. Linnetttreated some of these compounds using a different force field. He was able to account satisfactorily for 25 frequencies using 11 force constants. From our point of view the trouble with these results is that Linnett obtained a value for the C - C force constant in these acetylene derivatives which was different from that obtained by Crawford and Brinkley. For C - C in methyl cyanide for example, Linnett obtained... 

In this presentation, only the results of the reaction of silicon atoms with methyl chloride as the substrate molecule are discussed explicitly. In our full paper [lb] we show that matrix isolation techniques can be applied to uncover not only the intramolecular transformations of the triplet n-adducts T-5a-d, which are formed in the reaction of a Si atom with a single molecule of methyl halide, to the corresponding singlet halomethylsilylene S-la-d. If the concentration of the target molecule is raised, also intermolecular processes, like the addition of a second methyl halide molecule to the silylene intermediate under formation of dihalodimethylsilanes 8a-d via adducts 7a-d, can be revealed. 

The key elements of these carbonylation processes is the ability of a metal complex to undergo facile oxidative addition with methyl halide (especially iodide), carbon monoxide (CO) insertion into the methyl-metal bond, and reductive elimination of the acetyl group as the acetyl halide [3]. 

An oxidative addition of HCl to ReH(N2)(dppe)2 begins with protonation to give [ReH2(N2)(dppe)2]Cl. On heating in benzene with additional HCl, this intermediate is converted to ReHCl2(dppe)2. Methyl halides convert ReH(N2)(dppe)2 to ReX(N2)(dppe)2 (X = Br, I). Oxidative addition of CH3X followed by methane elimination is a likely mechanism. 

In addition to the regioselectively derivatized CDs, a number of statistically substituted CDs are in use. Highly water-soluble statistic derivatives are obtained by reaction of CDs with methyl halides [68], with epoxides (e.g., ethylene oxide, propylene oxide [69,70], or allyl glycidylether [71]), and with cyclic sulfates (e.g., butane sultone [72]). Statistical allyl ethers were converted to sulfonates by addition of sulfite [71], Monochlorotriazinyl-P-CD is another available reactive CD. Since these synthetic procedures are rather simple compared to the regioselective ones, many of these statistical compounds are available at the technical scale. 

If an organic chemist wanted to put a methyl group on a nucleophile, methyl iodide would most likely be the methylating agent used. Of the methyl halides, methyl iodide has the most easily displaced leaving group because 1 is the weakest base of the halide ions. In addition, methyl iodide is a liquid, so it is easier to handle than methyl bromide or methyl chloride. The reaction would be a simple Sn2 reaction. 

The yield from RX is CH3>1°>2°(>3°). Hence, to produce ether efficiently, a methyl halide or primary halide should be selected. The sodium alkoxides are made by the addition of sodium metal to alcohols ROH + Na RO" Na + JjHa. Due to the appreciable acidity of phenols, sodium phenoxides are made by the action of aqueous sodium hydroxide to phenols ... 

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