Alkoxy group

Smith and Dawson [3] determined traces of ether linkages in polyethylene glycol and polypropylene glycol by reacting the sample with hydrobromic acid then determining the dibromoethane and dibromopropane fission products by gas chromatography. 

The Zeisel method has been used to determine ether groups in cellulose and polyvinyl ethers [58]. 

Reproduced with permission from D.G. Anderson, K.E. Isakson, J.T. Vandeberg, M.Y.T. Jao, D.J. Tessari and L.C. Afremow, Analytical Chemistry, 1975, 47, 7, 1008.  

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In all cases examined the ( )-isomers of the allylic alcohols reacted satisfactorily in the asymmetric epoxidation step, whereas the epoxidations of the (Z)-isomers were intolerably slow or nonstereoselective. The eryfhro-isomers obtained from the ( )-allylic alcohols may, however, be epimerized in 95% yield to the more stable tlireo-isomers by treatment of the acetonides with potassium carbonate (6a). The competitive -elimination is suppressed by the acetonide protecting group because it maintains orthogonality between the enolate 7i-system and the 8-alkoxy group (cf the Baldwin rules, p. 316). 

Alkoxythiazoles are easily cleaved by acids yielding A-4-thiazoline-2-ones (36). C-5 Nitration of the thiazole ring is favored by the 2-alkoxy group (288. 297, 307). Recent kinetic investigations have shown that the rate enhancement is 3 log units (893). 

The reaction of amines with the 4-phenylazo derivative (228) results in their rearrangement into triazolines. Depending on the basicity of the amines and the size of the alkoxy group, three different triazolines (229. 230, and 231) are obtained (Scheme 117) (454. 459, 472). In all cases, the first step involves nucleophilic addition of the amine to the carbonyl group followed by ring opening and further ring closure. 

Any electron-attracting group, -NO2, -CN, -Ac, or -COjEt, on the a-carbon of the methine chain of a thiazole dye gives a bathochromic shift (120). A reverse effect is observed for an alkoxy group. 

In spite of the ene ending to its name polyethylene is much more closely related to alkanes than to alkenes It is simply a long chain of CH2 groups bearing at its ends an alkoxy group (from the initiator) or a carbon-carbon double bond... 

Disacchandes are carbohydrates that yield two monosaccharide molecules on hydroly SIS Structurally disaccharides are glycosides m which the alkoxy group attached to the anomeric carbon is derived from a second sugar molecule... 

Section 25 13 Glycosides are acetals compounds m which the anomenc hydroxyl group has been replaced by an alkoxy group Glycosides are easily prepared by allowing a carbohydrate and an alcohol to stand m the presence of an acid catalyst... 

Methoxy and alkoxy groups facilitate cross-linking at low temperatures. 

Alkoxy groups R -OR R= CHb or C2H5 or 0 Reaction with HI to produce Rl AgN03 Agl... 

With Lewis acids as catalysts, compounds containing more than one alkoxy group on a carbon atom add across vinyl ether double bonds. Acetals give 3-alkoxyacetals since the products are also acetals, they can react further with excess vinyl ether to give oligomers (228—230). Orthoformic esters give diacetals of malonaldehyde (231). With Lewis acids and mercuric salts as catalysts, vinyl ethers add in similar fashion to give acetals of 3-butenal (232,233). 

Acrylamide—acrylic polymers are made by free-radical polymerization of monomers containing the acryHc stmcture, where R is —H or —CH and is —NH2 or a substituted amide or the alkoxy group of an ester. 

The alkyl and alkoxy substituents of phosphate or phosphonate esters also affect the phosphorylating abiUty of the compound through steric and inductive effects. A satisfactory correlation has been developed between the quantitative measure of these effects, Tafts s O, and anticholinesterase activity as well as toxicity (33). Thus long-chain and highly branched alkyl and alkoxy groups attached to phosphoms promote high stabiUty and low biological activity. 

One of the most useful reactions in forming a P—C bond is the Michaehs-Arbusov reaction, which is a characteristic reaction of tricoordinate phosphoms compounds containing an alkoxy group (22). Alkylation of the electron pair is followed by rearrangement of the initial phosphonium salt. 

The reaction proceeds in a stepwise fashion and products with only one or two halogens can be produced by suitably limiting the reagent. Using alcohols, alkoxy groups are introduced. Either one or all three halogens can be replaced. 

Much work has been done on the structure of the metal alkoxides (49). The simple alkaU alkoxides have an ionic lattice and a layer stmcture, but alkaline earth alkoxides show more covalent character. The aluminum alkoxides have been thoroughly studied and there is no doubt as to their covalent nature the lower alkoxides are associated, even in solution and in the vapor phase. The degree of association depends on the bulkiness of the alkoxy group and can range from 2 to 4, eg, the freshly distilled isopropylate is trimeric (4) ... 

The estimation of alkoxy groups is not such a simple task. One method (26,68) involves hydrolysis and oxidation of the Hberated alcohol with excess standard potassium dichromate solution. The excess may then be estimated iodometrically. This method is suitable only for methoxides, ethoxides, and isopropoxides quantitative conversion to carbon dioxide, acetic acid, and acetone, respectively, takes place. An alternative method for ethoxides is oxidation followed by distillation, and titration of the Hberated acetic acid. 

For the higher alkoxy groups, standard carbon and hydrogen analysis may be used, although careful sample preparation is required because of the ease of hydrolysis. Quantitative vapor-phase chromatography of alcohol Hberated during hydrolysis may also be used, but care must be taken in this case to ensure that hydrolysis is complete before the estimation is carried out. 

Delignification Chemistty. The chemical mechanism of sulfite delignification is not fully understood. However, the chemistry of model compounds has been studied extensively, and attempts have been made to correlate the results with observations on the rates and conditions of delignification (61). The initial reaction is sulfonation of the aUphatic side chain, which occurs almost exclusively at the a-carbon by a nucleophilic substitution. The substitution displaces either a hydroxy or alkoxy group ... 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

Substitution of some of the alkoxy groups on the polytitanoxanes with glycols, P-diketones or P-ketoesters, fatty acids, diester phosphates or pyrophosphates, and sulfonic acids gives a group of products that are very effective surface-treating agents for carbon black, graphite, or fibers (32). 

Reactions with Alcohols. The tendency of titanium(IV) to reach coordination number six accounts for the rapid exchange of alkoxy groups with alcohols. Departure of an alkoxy group with the proton is the first step in the ultimate exchange of all four alkoxyls. The four-coordinated monomer is expected to react... 

The same products may be made from primary alkoxides by the violent reaction with elementary chlorine or bromine. A radical mechanism has been proposed to account for the oxidation of some of the alkoxy groups (54) ... 

In a given (RO) TiCl4 the alkoxy group can be exchanged by a higher alcohol if the resulting lower alcohol is removed by distillation (60). In the intermediate, HOR departs much more easily than HCl. 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

The orange-red titanium acetylacetone chelates are soluble in common solvents. These compounds are coordinately saturated (coordination number equals 6) and thus much more resistant to hydrolysis than the parent alkoxides (coordination number 4). The alkoxy groups are the moieties removed by hydrolysis. The initial product of hydrolysis is beheved to be the bis-hydroxy bis-acetylacetone titanate, (HO)2Ti(acac)2, which oligomerizes to a... 

Alternatively, a water-stable bis-acetylacetone titanate can be formed by replacing at least one of the alkoxy groups with an alkyloxyalkyleneoxy or alkyloxypolyalkyleneoxy group (94). 

Beginning with a mixture of tetraalkyl titanates, the resultant bis-ethyl acetoacetate contains a mixture of all possible combinations of alkoxy groups, resulting in a reduction in viscosity and improved cold-storage stabiHty of the product (97). 

Reactions at the C-5 position of the tetracycline molecule have been limited to the iatroduction of an alkoxy group (42) and the acetylation of the hydroxyl group (43) ia 5-hydroxytetracycline. Neither of these modifications improved the biological activity of the molecule. 

A lower alkyl or alkoxy group substituted in the ortho or meta position to an amino group may promote coupling. Good couplers are obtained from dimethylaruline when lower alkyl, lower alkoxy, or both groups are present in the 2- and 5-position. 

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