Availabilities, hydroxyl groups

Acylation (Section 25 22) Esterifi cation of the available hydroxyl groups occurs when carbohydrates are treated with acylating agents... 

Alkylation (Section 25 22) Alkyl halides react with carbohydrates to form ethers at the available hydroxyl groups An application of the Williamson ether synthesis to carbohydrates... 

Natural Ethoxylated Fats, Oils, and Waxes. Castor oil (qv) is a triglyceride high in ticinoleic esters. Ethoxylation in the presence of an alkaline catalyst to a polyoxyethylene content of 60—70 wt % yields water-soluble surfactants (Table 20). Because alkaline catalysts also effect transestenfication, ethoxylated castor oil surfactants are complex mixtures with components resulting from transesterrfication and subsequent ethoxylation at the available hydroxyl groups. The ethoxylates are pale amber Hquids of specific gravity just above 1.0 at room temperature. They are hydrophilic emulsifiers, dispersants, lubricants, and solubilizers used as textile additives and finishing agents, as well as in paper (qv) and leather (qv) manufacture. 

Etherification. The accessible, available hydroxyl groups on the 2, 3, and 6 positions of the anhydroglucose residue are quite reactive (40) and provide sites for much of the current modification of cotton ceUulose to impart special or value-added properties. The two most common classes into which modifications fall include etherification and esterification of the cotton ceUulose hydroxyls as weU as addition reactions with certain unsaturated compounds to produce ceUulose ethers (see Cellulose, ethers). One large class of ceUulose-reactive dyestuffs in commercial use attaches to the ceUulose through an alkaH-catalyzed etherification by nucleophilic attack of the chlorotriazine moiety of the dyestuff ... 

This paper examines two types of hydroxypropyl lignin based macromers, and these are illustrated schematically in Figure 1. Macromers with propylene oxide (PO) are formed by reducing the number of available hydroxyl groups on HPL followed by chain extension with PO and macromers with cellulose triacetate (CTA) are synthesized by attaching a monofunctional CTA chain to a limited number of terminal OH groups on HPL via a suitable grafting reaction. 

According to the work of Kozlov et al. [67] the viscosity of a 2% nitrocellulose (11.5% N) solution in acetone is decreased as a result of adding such electrolytes as lithium chloride up to a quantity equivalent to the number of available hydroxyl groups. The viscosity fell from 0.17 P to some 0.14-0.11 P. 

Fischer once termed hexoses monotonous because all five of the available hydroxyl groups give derivatives, with little differentiation in reactivity. He broke the monotony mainly through use of the isopropylidene derivatives, and thereby prepared the way for later developments. 

The teichoic acid which had not been subjected to ion-exchange chromatography contained D-alanine in characteristic, labile, ester linkage. It contained insufficient glucose to accommodate all of the alanine ester residues (alanine phosphorus ratio, 0.89 1), and the kinetics of the reaction with hydroxylamine indicated that all of the alanine is attached to the available hydroxyl groups at C-2 of glycerol residues. 

This process can be visualized as continuing until all available hydroxyl groups have been involved, leaving a residue which because of its high carbon content is difficultly combustible. 

The chemical reaction proceeds with the terminal isocyanate of the initial prepolymer reacting with the available hydroxyl groups of the diol. This is illustrated in Figure 2.26. 

Miller and Kotos [1990] applied this concept to modifying gamma-alumina membranes. The pore sizes of these membranes are modified by using the U ifunctional silane, tridecafluro-l,l,2,2-tetrahydrooctyM-trichlorosilane (abbreviated as TDFS), which has three reactive chlorine atoms. The reaction between the silane and the available hydroxyl groups on the membrane surface leads to the formation of Al-O-Si bonds and the release of HCl. The release of HCl in combination with the pressure measurement can be used to monitor the reaction. 

The preceding analysis suggests that water, indeed, penetrates throughout the amorphous regions of these materials and undergoes a specific interaction with available sorption sites, most likely the available hydroxyl groups on the anhydroglucose units. Differential heat of sorption results for various starches ... 

There are varying degrees of interaetion between fluids and the wood substanees. For example, water would be expeeted to form hydrogen bonds with available hydroxyl groups of the wood tissue. 

One of the essential factors governing the products of acetalation is the disposition of available hydroxyl groupings of the conceivable products obtained at equilibrium, the relative free-energies of the isomers will be decisive. This, in turn, will involve a consideration of ring strain, nonbonded interactions, and repulsions. 

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