Alkoxylation reaction

KTB and KTA are superior to alkaU metal hydrides for deprotonation reactions because of the good solubiUties, and because no hydrogen is produced or oil residue left upon reaction. Furthermore, reactions of KTA and KTB can be performed in hydrocarbon solvents as sometimes requited for mild and nonpolar reaction conditions. Potassium alkoxides are used in large quantities for addition, esterification, transesterification, isomerization, and alkoxylation reactions. 

Organic Reagents. Amine oxides are used ia synthetic organic chemistry ia the preparation of olefins, or phase-transfer catalysts (47), ia alkoxylation reactions (48), ia polymerization, and as oxidizing agents (49,50). 

This type of alkoxylation chemistry cannot be performed with conventional alkali metal hydroxide catalysts because the hydroxide will saponify the triglyceride ester groups under typical alkoxylation reaction conditions. Similar competitive hydrolysis occurs with alternative catalysts such as triflic acid or other Brpnsted acid/base catalysis. Efficient alkoxylation in the absence of significant side reactions requires a coordination catalyst such as the DMC catalyst zinc hexacyano-cobaltate. DMC catalysts have been under development for years [147-150], but have recently begun to gain more commercial implementation. The use of the DMC catalyst in combination with castor oil as an initiator has led to at least two lines of commercial products for the flexible foam market. Lupranol Balance 50 (BASF) and Multranol R-3524 and R-3525 (Bayer) are used for flexible slabstock foams and are produced by the direct alkoxylation of castor oil. 

The discovery of a different reaction mechanism of anodic methoxylations on BDD electrodes led to a closer investigation of electrosynthetic possibilities. First of all, BDD electrodes exhibit a 400- mV larger electrochemical window in methanol compared with graphite (Fig. 5.4). This opens access to a series of alkoxylation reactions which are not selective on conventional electrodes. 

These compounds can be prepared either by formation of the atrane framework at the central atom or by substitution reactions of other atranes. The most common method of the atrane fragment formation is frani-alkoxylation reactions that proceed under moderately mild conditions (equation 48)551.554-557 jjj jjjg following derivatives 188-191... 

Examples of amination and alkoxylation reactions are given in Scheme 21. Synthetic eqnivalents of ammonia, such as Ph2C=NH, can be used to prepare anilines and t-BuMe2SiONa reacts to give protected phenols. ... 

The activation treatment involves steeping cellulose (cotton or pulp fibers in sheet form) with cold 15 to 20% aqueous alkali for several hours. This alkali cellulose is subsequently reacted with reagents that consume alkali (Williamson synthesis) or alternatively in reactions in which alkali serves as catalyst (alkoxylation). Reactions are carried out between room temperature and 110 °C. Following reaction, cellulose ethers in solid fiber form (by virtue of being suspended in a small polar solvent such as isopropanol) are washed with aqueous alcohol, dried, and powdered by granulation (O Fig. 23). 

Alkoxylation reactions provide another route to C-0 bond formation.22 This reaction is limited in scope to activated aromatics because of alcohol oxidation, but a number of useful syntheses have come about. Recent papers have, for example, demonstrated that functionalized quinones can be synthesized by blocking the carbonyls in this fashion,21 and that 4,4-... 

Figure 13.2 Tertiary amines with high catalytic activity in alkoxylation reactions...

Unfortunately, it is a difference between a starter, such as nonylphenol, or a fatty alcohol, which have only one type of hydroxyl group and polyols. Some polyols used as starters for rigid polyether polyols have in the same molecule various types of hydroxyl groups (for example, primary hydroxyls and secondary hydroxyls) which do not have equivalent reactivities in the alkoxylation reactions. For example, sorbitol has two primary hydroxyls and four secondary hydroxyls, sucrose has three primary hydroxyls and five secondary hydroxyls. In both polyols, the secondary hydroxyls have different substituents and they are not totally equivalent. TMP, pentaeriythritol and dipentaerythritol have only one type of equivalent primary hydroxyl group. Thus, the initiation reaction (reaction of PO with hydroxyl groups of starter) is in fact the sum of the reactions of PO with each type of hydroxyl group of the starter ... 

The polyols for rigid foams (referred to as rigid polyols) discussed before (Chapters 13 and 14), are based on the alkoxylation of different polyols or polyamines, commercialised in a relatively high purity form. Some important starters for rigid polyols are obtained by the synthesis of the starter in situ, before the alkoxylation reaction, by the condensation reaction of some aromatic compounds (phenols, melamine and so on) with aldehydes (mainly formaldehyde), followed by the reaction of the resulting condensate with alkylene oxides. Some important rigid polyols based on the condensates mentioned are ... 

The anhydrised Mannich base is heated under nitrogen at 80-125 °C (preferably at 80-90 °C to avoid viscosity increase) and PO (or a mixture of PO-EO or EO) is added stepwise within 4-6 hours. The reaction does not need a catalyst. The alkoxylation reaction is catalysed just by the tertiary amino nitrogen formed as a consequence of the Mannich reaction. 

For Mannich polyols from phenol, the alkoxylation reaction of the corresponding Mannich base is presented in reaction 15.11. Of course, the Mannich base can have one or two aminomethyl groups or a mixture of these structures. 

During the alkoxylation reaction, PO or EO are added to all hydroxyl groups from the reaction system (phenolic and aliphatic hydroxyl groups), but firstly to the phenolic hydroxyl groups. Lignin-based polyester polyols formed by the reaction of lignin with e-caprolactone were developed [10, 12, 21, 22]. 

In Sections 20.1-20.4 the main reactions involved in the chemical recovery of PU wastes i.e., hydrolysis, glycolysis, aminolysis and alkoxylation reactions were presented. Several important processes for chemical recovery of PU polymers will be presented in the next chapters. 

A novel alkoxylation reaction has been observed by Schmid and coworkers (180) on compounds in the 12-methoxyaspidospermidine series. 

Diem et al. reported a mild alkoxylation reaction using trialkyloxonium tetrafluoroborate (Meerwein s salt) [7]. In this reaction. Proton Sponge (1) was found to be an effective base, as well as Hiinig s base (diisopropylethylamine) (Table 8.1). The reaction of (R)-(+)-l-phenylethyl alcohol with Meerwein s trimethyloxonium tetrafluoroborate (2.1 equiv.) and Proton Sponge (1) (2.1 equiv.) in dichloromethane at room temperature gave methyl ether in 69% yield without loss of optical purity (Table 8.1, run 1). (5)-(—)-2-Methyl-l-butanol was also methylated in 57% yield (run 3). 

With ordinary reaction catalysts such as conventional acids or bases, the products of the alkoxylation reactions are mixtures with a considerable range of... 

Further examples of synthetic application of the para-alkoxylation reaction include the preparation of dimethoxy ketal 231, which is an essential precursor in the enantioselective synthesis of the potent antifungal agent (-)-jesterone [297], the synthesis of various dimethoxy ketals of para- and ort/to-benzoquinones [298] and the methoxylation of various phenolic substrates, such as 232, using (diacetoxyiodo)benzene in methanol (Scheme 3.95) [299-301]. 

When alkoxide ion is present, the alkoxylation reactions proceed through its initial discharge... 

Although this alkoxylation reaction requires a three-step synthesis from PhSiHs, Woo and coworkers achieves straightforward one-pot Si-Si/Si-O dehydrocoupling and synthesis of aryltrihydrosilane using titanocenes and zirconocenes with red-aluminum, resulting in the one-pot synthesis of poly-(alkoxyarylsilane) under milder conditions with excellent total yields." " ... 

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