Etherification partial

Etherification. The reaction of alkyl haUdes with sugar polyols in the presence of aqueous alkaline reagents generally results in partial etherification. Thus, a tetraaHyl ether is formed on reaction of D-mannitol with aHyl bromide in the presence of 20% sodium hydroxide at 75°C (124). Treatment of this partial ether with metallic sodium to form an alcoholate, followed by reaction with additional aHyl bromide, leads to hexaaHyl D-mannitol (125). Complete methylation of D-mannitol occurs, however, by the action of dimethyl sulfate and sodium hydroxide (126). A mixture of tetra- and pentabutyloxymethyl ethers of D-mannitol results from the action of butyl chloromethyl ether (127). Completely substituted trimethylsilyl derivatives of polyols, distillable in vacuo, are prepared by interaction with trim ethyl chi oro s il an e in the presence of pyridine (128). Hexavinylmannitol is obtained from D-mannitol and acetylene at 25.31 MPa (250 atm) and 160°C (129). 

Partial etherification of the beech wood MGX with p-carboxybenzyl bromide in aqueous alkali yielded fully water-soluble xylan ethers with DS up to 0.25 without significant depolymerization the Mw determined by sedimentation velocity was 27 000 g/mol [400,401]. By combination of endo- 6-xylanase digestion and various ID- and 2D-NMR techniques, the distribution of the substituents was suggested to be blockwise rather than uniform. The derivatives exhibited remarkable emulsifying and protein foam-stabilizing activi-... 

Most of the selective-etherification studies on polysaccharides have been made with cellulose, and nearly all of them have involved quantitative separation of the D-glucose derivatives formed on hydrolysis of the partially substituted celluloses. In view of their stability, ethers of polysaccharides are particularly suited to this approach. 

The soluble hydroxymethyl compounds can be chemically modified, before crosslinking, by reaction with monofunctional compounds (e.g., by esterification or ether formation). The properties of the starting materials as well as the crosslinked end products can thereby be substantially altered. For example, by partial etherification with butanol the hydroxymethyl compounds, originally soluble only in polar solvents, become soluble also in nonpolar solvents (toluene), without losing their ability to undergo self-crosslinking. 

Cellulose may be converted from a water-insoluble polymer to a water-soluble polymer by the partial etherification of some of the hydroxyl groups by dimethyl sulfate. When the degree of substitution (DS) is 1.5 to 2.0, the hydrogen bonds are sufficiently weakened, and the methylcellulose is soluble in water. Carboxymethyl ethers, such as carboxymethylcellulose (CMC), are also water-soluble. The degree of solubility is related to the DS of the polymer and the pH of the solvent. 

Scheme 33. Coupling at the 6,6 -positions of partially protected sucrose by Williamson etherification.

Of the chemical methods to separate the azeotropic mixture of silicon tetrachloride and trimethylchlorosilane, etherification is the most convenient one. This method is based on the different activity of components in the reactions of partial etherification by alcohols or phenols. Silicon tetrachloride is the first to interact with alcohols or phenols, eventually forming tetraloxy- or tetraaroxysilanes ... 

Ethyl ether of orthosilicon acid (tetraethoxysilane) is most widely applied of all the ethers of orthosilicon acid because it is cheap, relatively easy to prepare and not toxic. Since the production of tetraethoxysilane uses the mixture of anhydrous and hydrous alcohol, etherification as a rule yields a mixture of tetraethoxysilane and ethylsilicates, the products of its partial hydrolysis and condensation. That is why we view below at the same time the technology to prepare tetraethoxysilane and ethylsilicate. 

Oligophenylethoxysiloxanes are obtained by the joint process of etherification and hydrolytic condensation of phenyltrichlorosilane. The degree of oligomer polymerisation depends on the amount of water and alcohol in the reaction. Apart from oligomers, the reaction forms products of partial hydrolytic condensation, such as 1,3-diphenyltetraethoxydisiloxane. 

Polymethylsiloxane varnishes are toluene-butanol solutions of the products of the hydrolytic condensation of methyltrichlorosilane, partially etherificated with butyl alcohol, whereas polymethylsilsesquioxane varnishes are toluene-acetone solutions of the products of the hydrolytic condensation of methyltrichlorosilane. 

The production of polymethylsiloxane varnishes comprises three main stages (Fig. 64) the partial etherification of methyltrichlorosilane with butyl alcohol the hydrolytic condensation of partially etherified methyltrichlorosilane the distillation of the solvent and preparation of the varnish. 

Methyltrichlorosilane is etherified in enameled hydrolyser 5, which is loaded with a necessary amount of methyltrichlorosilane (at least 99% of the main fraction) and toluene (half of the methyltrichlorosilane volume). The mixture is agitated for 30 minutes and checked for chlorine content (it should be 46.9 0.5%). Then the hydrolyser is filled with butyl alcohol at such speed that the temperature in the apparatus does not rise above 30 °C (for partial etherification one should take slightly more than 1 mole of C4H9OH per 1 mole of CH3SiCl3). 

After butyl alcohol has been introduced, the reactive mixture is heated to 60 5 °C within 2-3 hours and held at this temperature for 3-5 hours. The standing is finished when the chlorine content in silicon chloroethers (a byproduct of the partial etherification of methyltrichlorosilane) is 15-42% depending on the type of the varnish. The mixture is cooled to 20-30 °C by sending water into the jacket of the hydrolyser. The cooled chloroethers are sent through a siphon into weight batch box 6. 

The hydrolytic condensation of phenylethoxysilanes is carried out in butyl alcohol that is why at this stage we observe a partial re-etherification of phenylethoxysilanes with butyl alcohol and partial condensation of the re-etherification products. Generally, the process can be described by the following scheme ... 

Below let us use poly [4-[2-(hydroxyphenyl)propyl-2]-phenyl]phenyl siloxane as an example and illustrate the production of polyphenylsiloxanes from trialkoxyphenylsilane (in our case tributoxy-phenylsilane) synthesised by the second technique, the etherification of phenyltrichlorosilane. The production comprises the following main stages the synthesis of tributoxyphenylsilane and its partial hydrolytic condensation the re-etherification of polybutoxyphenylsiloxane with diphenylolpropane. 

Partial hydrolytic condensation can be carried out in the same apparatus 1. It is filled with a necessary amount of water within 0.5-1 hours, when the temperature of the reaction medium is 80-85 °C. The temperature in the reactor is increased to 95-100 °C, the reactive mixture is held at agitation for 7-8 hours and cooled down to 20-25 °C. The cooled polybutoxy-phenylsiloxane mixed with butyl alcohol, which has been formed in the process of hydrolytic condensation, is sent with vacuum through nutsch filter 5 into distillation tank 6. In the tank polybutoxyphenylsiloxane is clarified at 50-60 °C, poured into batch box 7 and sent with vacuum into reactor 8. Re-etherification is carried out in stainless steel apparatus 8 with a water vapour jacket and an anchor agitator. After loading polybutoxyphenylsiloxane, the apparatus is filled with a necessary amount of dipheny-... 

For example, polynonylsiloxane is synthesised by the hydrolytic condensation of partially etherified nonyltrichlorosilane and subsequent polycondensation of the obtained product. The production process comprises two main stages the partial etherification of nonyltrichlorosilane and the... 

The partial etherification of nonyltrichlorosilane with butyl alcohol is carried out at 75-80 °C and the mole ratio of the parent substances of 1 1.5. 

The mixer is loaded with nonyltrichlorosilane from batch box 8, the agitator is switched on and the mixture is agitated for 15-20 minutes. From container 4 butyl alcohol is sent into batch box 1. The ring jackets of tower 3 are filled with vapour when the temperatue in the tower rises to 75-80 °C, the toluene solution of nonyltrichlorosilane is sent from mixer 9 and butyl alcohol is sent from batch box 1 through fluoroplast nozzles in the bottom part of the tower. The solution of nonyltrichlorosilane and butyl alcohol is sent in the mole ratio of 1 1.5. The product of partial etherification is continuously withdrawn from the top of the tower through a run-down box into collector 10. 

Fig. 91. Production diagram of tetrabutoxytitanium by the continuous technique 1, 2, 6 - batch boxes 3 - tower for partial etherification 4, 10 - coolers 5 - trap 1,9- collectors 8 - bubble tower 11 - container 12 - nutsch filter...

Tower 3 receives titanium tetrachloride from batch box 2 for partial etherification. After the tower has been filled approximately to 1/5, the supply of TiCLt is not stopped and the tower receives butyl alcohol from batch box 1 at such speed that the temperature in the tower does not exceed 70 °C. 

The released hydrogen chloride passes through cooler 4 and trap 5 with butyl alcohol and is sent to absorption. The partially etherified product, dibutoxydichlorotitanium, is sent out of the tower into intermediate collector 7, which is filled with butyl alcohol from batch box 6. Out of collector 7 the mixture enters bubble tower 8 to complete etherification the reaction takes place in the presence of ammonia. A temperature of 50 °C is maintained in tower 8. 

Acetylation of 179, followed by partial hydrolysis (phenolic acetyl group) and etherification (CH2N2), gave derivative 180. By hydrogenolysis, the C-16—C-17 bond in 180 was opened after etherification the resulting phenol was transformed to 181 (see Scheme 33). Under modified hydrogenation conditions that N-10—C-l 1 bond can be hydrogenolyzed as well. 

Hydroxyl Reactivity. Tables 5 and 6 summarize the relative reactivities of hydroxyl groups observed in partial etherification of cellulose. Besides a distinctly high selectivity of the C6 OH group in tritylation, the relative reactivity of the 2-OH and 6-OH groups was considerably affected by the alkylation conditions, such as fiber swelling and the nature of etherifying conditions. 

---