Alcohols elimination

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

When applied to the synthesis of ethers, the reaction is effective only with primary alcohols. Elimination to form alkenes predominates with secondary and tertiary alcohols. 

Reactions of the hydrido(hydroxo) complex 2 with several substrates were examined (Scheme 6-14) [6]. The reactions are fairly complicated and several different types of reachons are observed depending on the substrate. Methyl acrylate and small Lewis bases such as CO, P(OMe)3, BuNC coordinate to the five-coordinated complex 2 affording the corresponding six-coordinate complexes. In reactions with the unsaturated bonds in dimethylacetylenedicarboxylate, carbon dioxide, phenylisocyanate indications for the addition across the O-H bond but not across the Os-OH bond were obtained. In reactions with olefins such as methyl vinyl ketone or allyl alcohol, elimination of a water molecule was observed to afford a hydrido metalla-cyclic compound or a hydrido (ethyl) complex. No OH insertion product was obtained. 

Final dilution to 60% ethyl alcohol eliminates protein clouds and extraction with petroleum ether removes oily and waxy substances. 

Imidazolidinium salts can also be transformed into the corresponding diamino ortho-esters by alkaline alkoxylate, and upon alcohol elimination at elevated temperature the imidazolidin-2-ylidenes can be trapped. The reaction of tria-zolium salts with sodium methanolate in methanol yields 5-methoxy-4,5-dihydro-IH-triazole which also eliminates methanol upon heating in vacuo. The resulting triazolin-5-ylidenes can either be isolated or trapped by an appropriate metal precursor [Eq. (19)]. Benzimidazolin-2-ylidenes are similarly accessible by this route. 

For 3-methoxydihydrobenzoxazine 276, trifluoroacetic acid (TEA) in dichloromethane at 0°C was used <1987M273>. />-Toluenesulfonic acid (PTSA) is suitable also for the cyclization stage, but the reaction must be followed carefully to avoid the alcohol elimination. The 3-methoxydihydrobenzoxazines 277 and 278 were prepared using PTSA in toluene at 75 °C <1986H(24)3483>. 

Condensation proceeds through either water elimination [Eq. (2)) or alcohol elimination 1 Eq. (3)). 

The current synthesis of ethyl alcohol eliminates sulfuric acid and uses phosphoric acid suspended on zeolite substrates. Zeohtes are porous aluminosilicate crystalline minerals. The use of phosphoric acid as a catalyst allows the direct hydrolysis of ethylene into ethyl alcohol C2H4 + H20 —> C2H5OH. Industrial alcohol is rendered inconsumable by adding a small amount of a poisonous substance such as methanol or acetone to it. Alcohol unfit for consumption because of a poisonous additive is termed denatured alcohol. 

Now let us consider esters in which the alcohol portion is the predominant portion of the molecule. Esters of fatty alcohols (except methyl esters) eliminate a molecule of acid in the same manner that alcohols eliminate water. A scheme similar to that described earlier for alcohols, involving a single hydrogen transfer to the alcohol oxygen of the ester, can be written. An alternative mechanism involves a hydride transfer to the carbonyl oxygen (McLafferty rearrangement). 

In contrast to the primary alcohols, tertiary alcohols eliminate water smoothly at 0°C in the presence of a 2-10 molar excess of hydrogen fluoride followed by polymerization.259 Reduced polymerization and satisfying yields of tertiary alkyl fluorides are achieved only at low temperatures (— 50 C). The reactivity of secondary aliphatic alcohols is thus interpreted to be between the other two types. High yields of alkyl fluorides are difficult to obtain because of the competing reactions and the effect of temperature on the equilibrium. 

FIGURE 21-23 Head-group attachment. The phospholipid head group is attached to a diacylglycerol by a phosphodiester bond, formed when phosphoric acid condenses with two alcohols, eliminating two molecules of H20. 

In the reaction of allylic alcohols, elimination of /1-hydrogen from an OH-bearing carbon takes place to give saturated carbonyl compounds, rather than arylated allylic alcohols [25,26]. The reaction of methallyl alcohol (43) with bromobenzene affords a-... 

Mann, G. Hartwig, J. F. Palladium alkoxides potential intermediacy in catalytic animation, reductive elimination of ethers, and catalytic etheration. Comments on alcohol elimination from Ir(III)./. Am. Chem. Soc. 1996, 118, 13109-13110. 

To complete this series of heterocumulene syntheses from carbonic acid derivatives, we here present the acid- and base-catalyzed alcohol elimination from carbamic acid esters (C, Figure 8.10) and the condensation of aniline and carbon disulfide to phenylisothiocyanate (F,... 

Other known methods for preparing O-alkyl enol ethers include, most notably, alcohol elimination from acetals, double bond isomeri2ation in allylic ethers, reduction of alkoxy enol phosphates, and phosphorane-based condensation approaches.5 These methods, however, suffer from poor stereoselectivity, low yields, or lack of generality, if not a combination of these drawbacks. 

Other pathways will continue to operate but, for plasma concentrations of the order of K, an apparently linear decrease in concentration with time will be seen. Thus, for alcohol in healthy adult males, has an average value of 82 lig/ml, and an average value of 202 qg/ml/hour. About 90% of alcohol elimination is usually by the capacity-limited alcohol dehydrogenase (oxidative) pathway, the remainder being by the kidneys and other routes of excretion. The renal clearance of alcohol depends on urine flow, and is approximately equal to urine flow rate, i.e. about 1 ml/min only a trace is eliminated via the lungs. For blood-alcohol concentrations of 100, 350, 1000, and 3500 qg/ml, the elimination of alcohol will be as shown in Table 3. As the concentration rises, so the elimination rate increases (but not proportionately) to reach a value of approximately V... 

The experimental. 4-factors for the alcohol elimination reactions are all in the range, log. 4 = 11.8 0.3, which agrees well with transition state estimates log4js, = 11.5+0.3. Activation entropies are therefore, AS —8 + 1.4 cal. deg mole This gives an average entropy loss of —2.7 eu per internal rotation restricted in the transition state. The experimental data for these reactions all seem quite reliable. Data for these reactions and the four-center reactions are given in Table 37. 

Inspection of Table 37 indicates that unlike the vinyl ether, ester and carboxylic acid elimination reactions, there is only a very minor effect on the alcohol elimination rates produced by substitution at the C-1 position. For alcohols with increasing C-1 substitution the ratio at 650 °K is... 

This is an alcohol elimination reaction with catalysis by Magnesium and using general base catalysis by the enzyme ... 

It has been demonstrated that the mechanism (see Section 3.1.4.1) for the reductive cleavage of the sulfoximine explains the mix of alkenes. Other effects, such as interconversion of the hydroxysulfox-imines, alcohol elimination or equilibration of the alkenes, were experimentally eliminated as the cause of the transicis ratios. ... 

Further cleavage of the chain with double bonds formed after the alcohol elimination explains the formation of some aromatic compounds such as benzene, toluene, styrene, benzaldehyde, etc. Two other common small molecules in the pyrolysate are phenol and the corresponding acid of the side chain substituent. 

The same bond as in the case of alcohol elimination can break with the formation of acetaldehyde, this time with the migration of a hydrogen from the side chain to the backbone of the polymer ... 

Body tissue possibly takes up benzyl alcohol rapidly and releases it slowly into the bloodstream. Rabbits when given 1 g (subcutaneously) of benzyl alcohol eliminated 300 00 mg of hippuric acid within 24 h. Rabbits eliminated 65.7% of a dose of 0.4 g of benzyl alcohol as hippuric acid in the urine. The plasma half-life of benzyl alcohol administered as a 2.5% solution in saline was found to be 1.5h in dogs injected intravenously at doses of 52 and 105 mgkg ... 

Salt-free sodium sulfonates. The blue dye formulated is required in pure, salt-free form for use in a procedure for determining blood volume. Since sodium acetate is moderately soluble in hot alcohol, elimination of sodium chloride can be accom-... 

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