Ethers, methyl acetal formation

Solvents that have been used with thiocyanogen include benzene, bromobenzene, carbon tetrachloride, chloroform, ether, ethylene bromide, carbon disulfide, petroleum ether, methyl acetate, nitromethane, and anhydrous formic and acetic acids. At low temperatures such solvents as saturated solutions of alkali thiocyanates in methanol or acetone can be used. The yield in the thiocyanation of amines is 20-30% higher when the reaction is carried out in a neutral medium like methanol rather than in acetic acid. The formation of a thiazole is also inhibited in a neutral solvent. Ether is usually not satisfactory because the solvent is attacked and because some of the amine is precipitated as the thiocyanate. On the other hand, thiocyanation of phenols appears to give better yields in acetic acid solution than in neutral solvents. 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-cataly2ed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] cataly2ed reaction, methyl acetate carbonylation is considered to go through formation of ethyUdene diacetate (33) ... 

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. 

ETHYLENE GLYCOL ETHYL MERCAPTAN DIMETHYL SULPHIDE ETHYL AMINE DIMETHYL AMIDE MONOETHANOLAMINE ETHYLENEDIAMINE ACRYLONITRILE PROPADIENE METHYL ACETYLENE ACROLEIN ACRYLIC ACID VINYL FORMATE ALLYL CHLORIDE 1 2 3-TRICHLOROPROPANE PROPIONITRILE CYCLOPROPANE PROPYLENE 1 2-DICHLOROPROPANE ACETONE ALLYL ALCOHOL PROPIONALDEHYDE PROPYLENE OXIDE VINYL METHYL ETHER PROPIONIC ACID ETHYL FORMATE METHYL ACETATE PROPYL CHLORIDE ISOPROPYL CHLORIDE PROPANE... 

Wender and coworkers conclude that cobalt-catalyzed benzyl alcohol homologation involves the intermediate formation of car-bonium ions (8). However, since the methyl cation (CH3+) is unstable and difficult to form (9), it is more likely that methanol homologation to ethanol proceeds via nucleophilic attack on a protonated methyl alcohol molecule. Protonated dimethyl ether and methyl acetate forms have been invoked also by Braca (10), along with the subsequent formation of methyl-ruthenium moieties, to describe ruthenium catalyzed homologation to ethyl acetate. 

Degradation of methyl terf-butyl ether by bifunctional aluminum in the presence of oxygen was investigated by Lien and Wilkin (2002). Bifunctional aluminum was synthesized by sulfating aluminum metal with sulfuric acid. When the initial methyl terf-butyl ether concentration was 14.4 mg/L, 90% of methyl ferf-butyl ether degraded within 24 h forming acetone, methyl acetate, tert-hniyX alcohol, and ferf-butyl formate. Carbon disulfide was tentatively identified as a reaction product by GC/MS. Product yields were 27.6% for acetone, 18.4% for methyl acetate, 21% for tert-hniyX alcohol, and 6.1% ferf-butyl formate. When the initial concentration of methyl tert-butyl ether was reduced to 1.4 mg/L, 99.5% of methyl terCbutyl ether reacted. Yields of acetone, methyl acetate, and /erf-butyl alcohol were 54.7,17.2, and 13.2, respectively. 

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

The formation of EDA in a one step reaction that involves the reductive carbonylation of methyl acetate has been achieved (equation 2) ( 1). Alternatively, the substrate of reductive carbonylation can be dimethyl ether instead of methyl acetate which simply integrates into the reaction an initial carbonylation step leading to EDA. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

Figure 7 shows the results of methyl acetate carbonylation in the presence of water. Methanol and dimethyl ether were formed up to 250 C suggesting that hydrolysis of methyl acetate proceeded. With increasing reaction temperature, the yield of acetic acid increased remarkably, while those of methanol and dimethyl ether decreased gradually. Figure 8 shows the effects of partial pressures of methyl iodide, CO, and methyl acetate in the presence of water. The rate of acetic acid formation was 1.0 and 2.7 order with respect to methyl iodide and CO, respectively. Thus, the formation of acetic acid from methyl acetate is highly dependent on the partial pressure of CO. This suggests that acetic acid is formed by hydrolysis of acetic anhydride (Equation 6) which is formed from methyl acetate and CO rather than by direct hydrolysis of methyl acetate. 

Industrial development of homologation processes for dimethyl ether, methyl formate, methyl acetate and acetic acid is likely only if they are integrated into a comprehensive plant for the production of C2 derivatives from syn-gas (Scheme 5). 

The methoxy species was detected by a reaction with acetic acid, ethyl iodide or water (or ethanol) giving methyl acetate, methyl ethyl ether or methanol, respectively. Formates were determined using dimethylsulfate (DMS). 

Construct a mechanism that shows why methyl tert-butyl ether (MTBE), a common gasoline additive, oxidizes in air to give formaldehyde as well as acetone, fert-butyl formate (HC(0)OC(CH 3),), and methyl acetate (CH3C(0)0CH3). 

Complex formation equilibria in binary mixtures of chloroform with dipropyl ether (PE), diisopropyl ether (IPE), methyl tert-butyl ether(MBE), tetrahydrofuran (THE), 1,4-dioxane (DOX), acetone (AC), and methyl acetate (MA) have been analyzed in detail. The complex formation equilibria in chloroform mixtures was compared to those previously examined for halothane (2-bromo-2-chloro-l,l,l-trifluoroethane) mixed with the same oxygenated solvents. It was found that the H-bonds formed by halothane are stronger than those formed by chloroform (Dohnal and Costas, 1996). 

Similarly with the raising of the b.p. in violet or reddish-violet soln. of iodine in benzophenone, carbon disulphide, ethyl chloride, chloroform, carbon tetrachloride, ethylene chloride or benzene or in brown soln. of ethyl alcohol, methyl alcohol, thymol, ethyl ether, methylal, or acetone. The values for the last three solvents were rather low, presumably because of the chemical action of solute on solvent. High values with benzene are attributed to the formation of a solid soln. of solvent and solid. Confirmatory results were found by J. Hertz with naphthalene, and by E. Beckmann and P. Wantig with pyridine. The results by I. von Ostromisslensky (o-nitrotoluene), by G. Kriiss and E. Thiele (glacial acetic acid), and by H. Gautier and G. Charpy indicate polymerization, but they are not considered to be reliable. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Whereas the C2—C4 alcohols are not carboxylated under the usual Koch-Haaf conditions, carboxylation can be achieved in the HF-SbF5 superacid system under extremely mild conditions.400 Moreover, Olah and co-workers401 have shown that even methyl alcohol and dimethyl ether can be carboxylated with the superacidic HF-BF3 system to form methyl acetate and acetic acid. In the carboxylation of methyl alcohol the quantity of acetic acid increased at the expense of methyl acetate with increase in reaction time and temperature. The quantity of the byproduct dimethyl ether, in turn, decreased. Dimethyl ether gave the desired products in about 90% yield at 250°C (90% conversion, catalyst/substrate ratio =1 1, 6h). On the basis of experimental observations, first methyl alcohol is dehydrated to dimethyl ether. Protonated dimethyl ether then reacts with CO to yield methyl acetate [Eq. (5.154)]. The most probable pathway suggested to explain the formation of acetic acid involves the intermediate formation of acetic anhydride through acid-catalyzed ester cleavage without the intervention of CO followed by cleavage with HF [Eq. (5.155)]. 

This section deals only with solvents whose reduction products are insoluble in the presence of lithium ions. The list includes open chain ethers such as diethyl ether, dimethoxy ethane, and other polyethers of the glyme family cyclic ethers such as THF, 2Me-THF, and 1,4-dioxane cyclic ketals such as 1,3-dioxolane and 1,3-dioxane, esters such as y-butyrolactone and methyl formate and alkyl carbonates such as PC, EC, DMC, and ethylmethyl carbonate. This list excludes the esters, ethyl and methyl acetates, and diethyl carbonate, whose reduction products are soluble in them (in spite of the presence of Li ions). Solutions of solvents such as acetonitrile and dimethyl formamide are also not included in this section for the same reasons. Figure 6 presents typical steady state voltammo-grams obtained with gold, platinum, and silver electrodes in Li salt solutions in which solvent reduction products are formed and precipitate at potentials above that of lithium metal deposition. These voltammograms are typical of the above-mentioned solvent groups and are characterized by the following features ... 

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