Eliminations dehydration

Dihydropyrans may be transformed to pyrans by dehydrogenation, dehydration, elimination of an alcohol or a carboxylic acid molecule, as well as by dehydrochlorination. 

It seems likely that this dehydrative elimination proceeds via the inverted iodide 26 (Scheme 8.12),13 although this intermediate was never detected in the reaction mixture. 

An alcohol is converted into an alkene by dehydration elimination of a molecule of water. Dehydration requires the presence of an acid and the application of heat. It is generally carried out in either of two ways (a) heating the... 

Often, the Michael reaction is followed by an aldol reaction, a substitution, or another Michael reaction. For example, the Robinson annulation consists of a Michael reaction, an aldol reaction, and a dehydration ( -elimination). 

Fig. 4.12 Diagenetic and catagenetic transformation of steroids. The precursor sterols are gradually transformed during diagenesis into saturated hydrocarbons by dehydration (elimination of water) and hydrogenation of the double bonds. At higher temperatures, during catagenesis, the thermodynamically most stable stereoisomers are formed. Alternatively, dehydration leads to aromatic steroid hydrocarbons which are stable enough to occur in crude oils (after Rullkotter 2001). See text for detailed description of the reaction sequences.

Cyclohexene will undergo an ozonolysis reaction to yield adipic acid upon oxidative workup. Cyclohexene is produced from cyclohexanol by a dehydration (elimination) reaction. The synthesis of adipic acid from cyclohexanol is... 

The vOH absorption of the liberated silanols appears at 3740 cm for samples G and P (Figure 26.3, curve b-a) correlated to the decrease of the shoulder at 5315 cm A further dehydration eliminates water molecules H-bonded through their two OH groups (22) and... 

Dehydrative elimination of hydroxyl groups is well known from the enzymatic conversion of saturated to monounsaturated fatty acids. Incubation of cholic acid with rat feces under anaerobic conditions gives a mixture of 7-deoxy products, which were presumed to have arisen through dehydration of the 7a -hydroxyl group, followed... 

Dehydration Elimination of a molecule of water from a compound. 

Bronsted Acids. Sulfuric acid (H2SO4) is an inexpensive, easy to handle protic acid used widely as catalyst in hydrolysis, hydration and dehydration, elimination, substitution, and rearrangements. It also catalyzes aromatic electrophilic substitutions mostly Friedel-Crafts acylations and alkylations (22). A very important application of sulfuric acid is its use in commercial isoalkane-alkene alkylation technologies. These commercial processes are still based on the use of sulfuric acid (and hydrogen fluoride) catalysts (23). 

Under the conditions used in the current experiment, dehydration-elimination rapidly follows the initial nucleophilic addition with formation of the benzylidene intermediate. The mechanism is shown here ... 

An alcohol undergoes dehydration (elimination of a water molecule) when it is heated with an acid. 

Oxirans. - Treatment of methyl 4,6-0-benzylidene-a-D-glucopyranoside with a mixture of diethyl carbonate and potassium carbonate in DMF has afforded directly a new simple synthesis of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside. The corresponding 2,3-cyclic carbonate is postulated as an intomediate. Some carbohydrate examples have been published of the use of sodium hydride and p-toluenesulfonyl chloride for the conversion of 1,2-diols to epoxides. Simple routes to the Cemy epoxides 6 and 7 finom D-glucal have been develc red (Scheme 1). In this scheme the flrst step involves a dehydration elimination with allylic rearrangement Syntheses of methyl 2,3-anhydro-a- and L-OTthiofuranoside have been reported. Some nitro-sugar epoxides are mentioned in Chapter 10. 

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