Ethanol elimination reaction

I.R. spectrum of heat-treated 4,4 -dibenzamido-6-ethoxycarbnyl benzanilide(Fig. 3) showed a strong lacton carbonyl absorption band at 1,746 cm and ether absorption band at 1,053 cm, suggesting the formation of benzoxazinone derivative by the ethanol elimination reaction between ethoxycarbonyl group and amide bond. 

Alcohols undergo dehydration in supercritical and hot water (41). Tertiary alcohols require no catalyst, but secondary and primary alcohols require an acid catalyst. With 0.01 MH2SO4 as a catalyst, ethanol eliminates water at 385°C and 34.5 MPa to form ethene. Reaction occurs in tens of seconds. Only a small amount of diethyl ether forms as a side reaction. 

The two most common elimination reactions arc dehydroUalogenalion—the loss of HX from an alkyl halide—and dehydration—(he loss of water from an alcohol. Dehydrohalogenation usually occurs by reaction of an alkyl halide with strong base such as potassium hydroxide. For example, bromocvclohexane yields cyclohexene when treated with KOH in ethanol solution. 

One problem with elimination reactions is that mixtures of products are often formed. For example, treatment of 2-bromo-2-methylbutane with KOH in ethanol yields a mixture of two alkene products. What are their likely structures ... 

Figure 11.22 Elimination reactions of menthyl chloride. E2 conditions (strong base in 100% ethanol) lead to 2-menthene through an anti periplanar elimination, whereas El conditions (dilute base in 80% aqueous ethanol) lead to a mixture of 2-menthene and 3-menthene.

An elimination reaction is, in a sense, the reverse of an addition reaction. It involves the elimination of two groups from adjacent carbon atoms, converting a saturated molecule into one that is unsaturated. An example is the dehydration of ethanol, which occurs when it is heated with sulfuric acid ... 

The states of reactants and products are often not given for organic reactions, because the reaction may take place at the surface of a catalyst or it may take place in a nonaqueous solvent, as here. The reaction is another example of an elimination reaction and is carried out in hot ethanol, with sodium ethoxide, NaCH CH,0, as the reagent. Some Cl I3CH2CH=CH2 is also formed in this reaction. 

The El reactions can involve ion pairs, just as is true for S l reactions (p. 398), This effect is naturally greatest for nondissociating solvents it is least in water, greater in ethanol, and greater still in acetic acid. It has been proposed that the ion-pair mechanism (p. 400) extends to elimination reactions too, and that the S l, Sn2, El, and E2 mechanisms possess in common an ion-pair intermediate, at least occasionally. ... 

With ethanolic potassium hydroxide, an elimination reaction occurs, producing an alkene. 

Reiter and co-workers found in the course of their extended research on fused [l,2,4]triazines <1994JHC997> that the N-protected methylthiotriazine derivative 110 when reacted with carbon disulfide under strongly basic conditions yields a mixture of two products 111 and 112. When this mixture was treated with dibromomethane, product 113 was easily removed from the reaction mixture, and workup of the mother liquor allowed the isolation of the [l,2,4]triazolo[l,5-c][l,3,5]thiadiazine derivative 114 in 49% yield (Scheme 21). The same authors carried out ring closure of the ring-closed semithiocarbazide 115 to the triazolothiadiazine derivative 118 as shown in Scheme 21 <1997JHC1575>. The starting compound was treated with triethyl orthoformiate. The authors assume that first intermediate 116 is formed which cyclizes to a second intermediate 117 and, finally, ethanol elimination yields the isolated product 118. 

Kluger and Brandi (1986b) also studied the decarboxylation and base-catalysed elimination reactions of lactylthiamin, the adduct of pyruvate and thiamin (Scheme 2). These reactions are nonenzymic models for reactions of the intermediates formed during the reaction catalysed by the enzyme pyruvate decarboxylase. The secondary j3-deuterium KIE for the decarboxylation was found to be 1.09 at pH 3.8 in 0.5 mol dm-3 sodium acetate at 25°C. In the less polar medium, 38% ethanolic aqueous sodium acetate, chosen to mimic the nonpolar reactive site in the enzyme, the reaction is significantly faster but the KIE was, within experimental error, identical to the KIE found in water. This clearly demonstrates that the stabilization of the transition state by hyperconjugation is unaffected by the change in solvent. 

Saunders and co-workers (Amin et al., 1990) used E2 elimination reactions in the p-substituted 2-phenylethyl system to test the new criteria for tunnelling suggested by the above calculations. The actual substrates and base/solvent systems they used were (2-phenylethyl-2-f)-trimethylammonium bromide, [19], with sodium ethoxide in ethanol, 2-phenylethyl-2-f bromide, [20], with potassium t-butoxide in t-butyl alcohol and 2-(p-chlorophenyl)ethyl-2-f tosylate, [21], with potassium t-butoxide in t-butyl alcohol. When equation (57) was applied to the experimental secondary (kB/ S) KIEs in Table 39, the calculated /th h KIEs were 1.106 0.033 and 1.092 0.026 for [19] and [21],... 

Monohaloalkanes can undergo elimination reactions when they are with ethanolic potassium (or sodium) hydroxide, l.e. a solution of potr hydroxide in ethanol. For example, when 2-bromopropane is heated Wi potassium hydroxide, the alkene propene is formed ... 

This reaction is achieved by heating the monohaloalkane under reflux with ethanollc potassium (or sodium) hydroxide, i.e. potassium (or sodium) hydroxide dissolved in ethanol. The reaction is referred to as a base-induced elimination reaction and to demonstrate more clearly the role of the base in the reaction, it is worth considering the mechanism involved. This is illustrated for the reaction between 2-bromopropane and ethanolic potassium hydroxide ... 

Use has been made of the bond cleavage processes initiated by an adjacent carbonyl function for the modification of steroidial ketols such as 18 [97], Reduction in ethanol eliminates the hydroxyl function and in the same reaction, the carbonyl function is reduced to a secondary alcohol. In compound 19 where there are several groups to act as electrophores, carbon-oxygen bond cleavage is initiated from the most easily reduced dienone function [98], Cleavage of the carbon-oxygen bond in an a-acetoxycarbonyl function is achievable in good yields from multifunctional compounds such as the sesquiterpene taxol [99]. 

Elimination reactions are considered when simple, volatile haloacetylenes are to be prepared. Dichlaroacetylene. far example, has been prepared as an ethereal solution [124] (the undiluted compound is highly explosive) by treating CljC CHCl with KOH at 200 C. Dibromo-acetylene is formed under milder conditions, namely from Br2C=CHBr and ethanolic... 

During an elimination reaction, atoms are removed, or eliminated, from adjacent carbons on a carbon chain, producing a small molecule, which is often water. A double bond forms between the adjacent carbons, producing an alkene. For example, ethyl alcohol (ethanol) can undergo an elimination reaction to form ethylene by the loss of H and OH, which form H2O (water). 

The El reaction involves the formation of a planar carbocation intermediate. Therefore, both syn and anti elimination can occur. If an elimination reaction removes two substituents from the same side of the C—C bond, the reaction is called a syn elimination. When the substituents are removed from opposite sides of the C—C bond, the reaction is called an anti elimination. Thus, depending on the substrates El reaction forms a mixture of cis (Z) and trans (E) products. For example, tert-hutyl bromide (3° alkyl halide) reacts with water to form 2-methylpropene, following an El mechanism. The reaction requires a good ionizing solvent and a weak base. When the carbocation is formed, SnI and El processes compete with each other, and often mixtures of elimination and substitution products occur. The reaction of t-butyl bromide and ethanol gives major product via El and minor product via SnI-... 

Conversion of sugar phenylhydrazones into olefinic azo-sugars on treatment with acetic anhydride and pyridine was shown by Wolfrom and co-workers (28) (The acetylated forms of the acyclic phenylhydrazones of D-glucose, D-mannose, and D-galactose readily lose the elements of acetic acid to yield 1-phenylazo-frans-l-hexenetetrol tetraacetate when treated with warm aqueous ethanol (28, 30). It is assumed that atmospheric oxygen partakes in this elimination reaction.) This is a special case of base catalyzed -elimination reactions of the type proposed by Isbell in 1943 ( 31), involving consecutive electron displacement (which actu-... 

The uncatalyzed H02 elimination from the peroxyl radical derived from methanol is too slow to be measured at room temperature (k < 10 s-1). That derived from ethanol eliminates H02" with k = 52 s and that derived from isopropyl alcohol undergoes an even faster elimination of HOj (k = 665 s-1). The activation energies are,T —60 kj. mol-1. If OH - acts as the base, reaction 38 occurs at rates that are near to diffusion-controlled. The catalysis by phosphate is three orders of magnitude slower. 

The reaction of (-)-menthyl chloride with sodium diphenylphosphide in tetra-hydrofuran requires 48-54 hr at reflux temperature for completion. The elimination side reaction is still observed. However, by-products (isomeric menthenes and diphenylphosphine) arising from the elimination reaction are easily removed by distillation. The overall conversion of (-)-menthyl chloride to (+)-NMDPP is about 34%, not counting the (+)-NMDPP oxide produced during a typical work-up. The (+)-NMDPP ligand is rather sensitive to air oxidation in solution and (+)-NMDPP oxide can be a very tenacious impurity, but careful crystallization of the phosphine from deoxygenated ethanol gives (+)-NMDPP in 95% (or higher) purity. 

What product would be expected from the elimination reaction of (l/ ,25j-l-bromo-1,2-diphenylpropane using sodium ethoxide in ethanol as the solvent ... 

The DNA sequencing chemistry begins with a base-modification reaction, the extent of which determines the frequency of DNA cleavage in the subsequent phosphate-elimination reaction. The number of bases modified in each molecule depends on the concentration of dimethylsulphate (G and G A reactions) and hydrazine (C T reactions) as well as the temperature and duration of the reaction. For speed and convenience the Maxam-Gilbert procedure makes use of temperature shifts and dilution to control the rate and extent of these reactions. The reagents are mixed at 0°C, incubated at 20°C for the required time and the DNA precipitated with cold sodium acetate and ethanol to slow down or halt the reaction. A fixed concentration of the different reagents is usually used so the main factor determining the extent of reaction is the time of incubation at 20°C. 

Draw the R enantiomer of D. Predict the products of reaction of D with (a) HBr (b) product of (a) + aqueous ethanol. Describe the reactivity of the -Cl atom in substitution and elimination reactions. 

N-bridging cyanate in low yields (17-23% after heating for 24 h Scheme 11). Conversion was found to proceed at comparable rates in ethanol or acetonitrile, and it was thus concluded that hydrolytic processes by traces of water do not play a role. Cyanate formation also was observed with Af-methylurea or 7/,7/-dimethylurea, but not with Af,A -dimethylurea or tetramethylurea, which shows that at least one NH2 group is essential for the elimination reaction to occur. A possible interpretation is that bridging of urea over the binuclear core through its O atom and one amino N atom is a key step for the conversion (58). This finding is in line with the discovery of urea-to-cyanate transformation for several pyrazolate-based dinickel complexes with urea bound in the N,0-bridging mode (see below). 

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