Etherification preferential

Sucrose Ethers. Being next to the anomeric center and intramolecularly hydrogen-bonded, the 2 -OH of sucrose is the most acidic, which means it is deprotonated first under alkaline conditions, and thus preferentially yields to etherification. Benzylation with NaH/benzylbromide in DMF, for example, results in an 11 2 1 mixture of 2 -(9-benzyl-sucrose (Figure 2.8) and its 1-0- and 3 -0-isomers. Because the former is readily accessible, it proved to be a versatile intermediate for the generation of 2 -modified sucroses, for example, the 2 -keto and 2 -deoxy derivatives as well as sucrosamine (2 -amino-2 -deoxy-sucrose), whose application profiles remain to be investigated. 

The discrepancies among reported data, besides possibly being caused by different analytic techniques employed, may be partly attributed to variations in the alkali concentration used as shown in Fig. 1. Rammas and Samuelson [197] also demonstrated that the reactivity of the 2-OH and 6-OH with ethylene oxide was quite comparable in dilute alkali and that the C6 hydroxyethylation was preferentially promoted by an increase in the alkali concentration. In etherification of cotton cellulose with sodium 2-aminoethyl sulfate [192], sodium allyl sulfate [193], or acrylamide [194], the 6-OH group was generally found to be more reactive than the 2-OH group. 

By the use of glycidol with nonylphenol the final product has proved of value as an emulsifier for stable aqueous acrylic polymers. Thus the reaction of excess glycidol with nonylphenol in toluene solution in the presence of ptassium hydroxide was described to give an hydoxypropoxylate (ref. 29). In the depicted reaction preferential etherification of the primary hydroxyl group takes place although it is probable that complex mixtures result in practice. 

Coumaric acid 28 presents a more ambitious problem because difTerential protection of two competing anionic sites is to be observed In the absence of 24 any possible esterification and etherification product is formed but adding a slight excess of host 24 switches the reaction paths to the exclusive production of the ester. The absolute reaction rate drops considerably indicating that host-guest complexation effects both reaction centers of the substrate. Nevertheless the differences in their reactivities are stressed by virtue of this dynamic protection preferentially at the phenolate thus enabling the enhancement of reaction selectivity. 

Removal of an aromatic methylenedioxy grotgf. This reaction can be carried out in three steps. Treatment with boron trichloride is known to cleave methylenedioxy groups preferentially (4, 43). The catechol group is then removed by etherification with S-chloro-l-phenyl-l-Zf-tetrazole and hydrogenolysis of the ether, An example is formulated. ... 

---