Etherification

Etherification procedures for alditols are the same as those for the other carbohydrates (Chapter VII). Sometimes, however, the attainment of fully etherified products may be difficult. Mannitol, for example, could not be converted to the hexamethyl ether despite repeated treatment with methyl iodide and silver oxide 116) or with methyl sulfate and alkali 117). 

Etherification is defined as the process of converting a substance (as an alcohol or phenol) into an ether that is formed by treating alkali cellulose with a variety of reagents. Etherification requires ionisation of hydroxyl, i.e., C-OH C-O.  

Hydroxy alkyl Hydroxyethyl cellulose Ethylene oxide 

Most ethers are water soluble and are used as thickeners in foods, cosmetics, pharmaceuticals, paints, etc. Critical properties of ethers include solubility, water-binding capacity, nontoxicity, and chemical stabihty. Degree of substitution (DS) determines properties of ethers that is the average number of -OHs substituted on anhydroglucose unit. Table 21.3 shows some of cellulose ether derivatives. 

Carboxymethyl cellulose (CMC) is the most important cellulose ether commercially. Its DS is 0.4-1.4. DS more than 0.6-0.8 gives a good water solubility. Carboxymethyl cellulose is one of the important modified celluloses that is widely used as an additive in industries. It possesses advantageous properties, especially solubility in water, immiscibility in oil and organic solvency, which makes it act as a multifunction agent. Therefore, it functions as stabilizer, thickener, binder and suspension agent in industries such as food and pharmaceutical. Hence, analysis of the CMC production process has been studied by researchers in order to enhance the efficiency of the process to achieve specific properties of CMC needed. There are many published works about CMC. For example, optimization of carboxymethyl cellulose production from etherification cellulose has been studied by Muei in 2010 [33]. 

The effect of methycellulose coating on the storage life of nectarine Var. Rafati was evaluated by Mizani et al. in 2009. The results showed that coating may increase overall acceptability, reduce weight loss in nectarine and increase the quality and shelf life of fruits [34]. 

Another important etherification is the palladium-catalyzed telomerization of glycerol with butadiene yielding octadienyl ethers of glycerol, which can be used as starting materials for detergents [51, 52]. 

Because of the high stability of the ether function, etherification of unprotected sucrose leads to a kinetic distribution of products directly reflecting the relative reactivity of the hydroxyl groups. This reaction is therefore the best probe for reactivity studies at least for discussing the relative rates of the first substitution. The following substitutions are more difficult to compare, since supplemental factors (electronic and steric) arising from the first substitution interfere with the natural reactivity order of unprotected sucrose. 

However, when bulky electrophilic species are used, such as chlorotrimethylsi-lane or highly substituted silyl chlorides, the primary alcohols at positions 6 and 6 react faster, the more hindered OH-T being less reactive because of its proximity to the quaternary carbon atom C-2.63 65 The trisilyl ether of all three primary OH groups is formed when tcrt-b u ty 1 d i phenylsilyl chloride (TBDPSC1) is used in excess. In the presence of 1.1 equiv. of TBDPSC, significant regio-selectivity is observed in favor of 6-OH, since the 6 -monoether can be obtained 

Substrate Alkyl Halide Product Distribution at C-positions (%) Yield (%) 

The regiochemical outcome of this reaction has been compared for sucrose and trehalose. This pointed out the higher reactivity at 0-2 in sucrose, with 76% substitution at 0-2 of the glucose moiety, as compared with 24% for trehalose (Table II, entries 2 and 3).74 The relative proportions of ethers at positions 3, 4, and 6 of the glucose moiety of sucrose or trehalose are identical, within experimental error (entries 4 and 5). 

The reaction of sucrose with propylene oxide in aqueous basic medium affords 2-hydroxypropyl ethers.76 Similar conditions gave sucrose glycerol-sucrose hybrids by reaction with glycidol.77 Polymeric resins are obtained, starting from sucrose or partially esterified sucrose, when diepoxides are used.78,79 

A very effective method to hydrophobize the surface of MFC is etherification of the hydroxyl functions with alkyl silanes. Both chlorosilanes and alkoxysilanes react readily with the hydroxyl functions of cellulose. 

Grunert and Winter [19] have described topochemical sUylation of BC nanocrystals with a typical cross-section 8 x 50 nm and a few hundred to several thousand nanometers in length The crystals were treated with hexamethyldisilazane in formamide, resulting in an average DS of 0.49. 

The reactions of the phenolic aldehydes may be conveniently grouped under etherification of the phenolic hydroxyl group, replacement of the aldehyde group and condensation reaction of the latter. 

2-Methoxymethoxybenzaldehyde was formed in 90% yield by the gradual treatment of salicylaldehyde, methylal and dimethylformamide in toluene with phosphorus oxychloride at 65°C during maintenance of a gentle reflux, which was continued after completion of the addition for 2 hours followed by work-up by pouring the mixture into ice-cold sodium hydroxide solution (ref.61). 

By passage of difluorochloromethane through an aqueous solution of salicylaldehyde in sodium hydroxide at 60 C, 2-difluoromethoxybenzaldehyde was formed in 90% yield (ref.62). 

3-Hydroxybenzaldehyde, 1-bromodecane and caesium carbonate in dimethylformamide when reacted at 80°C during 16 hours gave the 

Salicylaldehyde in aqueous solution upon addition to an aqueous solution of barbituric acid afforded a precipitate after stirring for 5-10 mins, which in hot acetic acid/acetic anhydride (9 1) gave in 50% yield 2H-chromeno[2,3-d]-pyrimidine-2,4(3H)-dione (ref.65). 

The products are then dissolved in aqueous alkali and alkylated at 40-50 °C for 30 min. Higher alkyl halides react with starch in aqueous alkali,705 but the use of high pressure is recommended.706 It is beneficial to soak starch in alkali prior to alkylation, arylation, or aralkylation. The use of ammonium hydroxide instead of NaOH for this purpose has been patented.707 The amount of alkali can be decreased when starch used for alkylation is precipitated from 33% aqueous chloral solution.708 

Fully alkylated starches are insoluble in water but are soluble in many polar nonaqueous and nonpolar solvents. Starch alkylated to a lower extent retains its water solubility but is also soluble in alcohols and chloroform. The solutions have a micellar character.741 Decrease in the softening points of alkyl starch ethers as the length of the alkyl chains increased is observed.706 The solubility of etherified starches depends also on which etherifying agent is applied. 

Alkylated starch can be fragmented by acetolysis into water soluble tri- and tetra-saccharides.742 Formic acid, together with a small amount of acetyl chloride, may be used instead.743 Alkyl a-D-glucosides can be prepared by treating starch with hydrogen chloride a solution of hydrochloride in a simple alcohol.744 

The chemistry of starch ethers has progressed with the use of a greater variety of alkylating agents, for instance, ethylene oxide,745 chloroacetic acid, epichloro-hydrin, vinyl monomers, and other alkylating agents.746 

260-270 °C, whereas the com starch derivative only turned brown at this temperature. Further allylation led to diallyl ethers.748-752 For this purpose, an acetone solution of starch acetate in a 50% solution of NaOH containing allyl bromide was boiled or heated in an autoclave at 80 °C. These procedures were then improved by using either butanone and KOFI753 or 1,4-dioxane and NaOH.754 Di-O-allyIstarch is a soft, gummy product that is soluble in most of organic solvents except for aliphatic hydrocarbons. This solubility is lost after exposure of diallyl starch to air.748 It can also be hardened by the addition Co(II) octanoate or Co(II) naphthenate.755 

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The potential advantages of LPG concern essentially the environmental aspects. LPG s are simple mixtures of 3- and 4-carbon-atom hydrocarbons with few contaminants (very low sulfur content). LPG s contain no noxious additives such as lead and their exhaust emissions have little or no toxicity because aromatics are absent. This type of fuel also benefits often enough from a lower taxation. In spite of that, the use of LPG motor fuel remains static in France, if not on a slightly downward trend. There are several reasons for this situation little interest from automobile manufacturers, reluctance on the part of automobile customers, competition in the refining industry for other uses of and fractions, (alkylation, etherification, direct addition into the gasoline pool). However, in 1993 this subject seems to have received more interest (Hublin et al., 1993). 

Table 10.7 shows the typical composition of a feedstock to an etherification unit and the average product properties obtained. 

Furthermore, the major problem of reducing aromatics is focused around gasoline production. Catalytic reforming could decrease in capacity and severity. Catalytic cracking will have to be oriented towards light olefins production. Etherification, alkylation and oligomerization units will undergo capacity increases. 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

Ether alcohols Ether formation Ether hydroperoxides Etherification... 

Cellulosics. CeUulosic adhesives are obtained by modification of cellulose [9004-34-6] (qv) which comes from cotton linters and wood pulp. Cellulose can be nitrated to provide cellulose nitrate [9004-70-0] which is soluble in organic solvents. When cellulose nitrate is dissolved in amyl acetate [628-63-7] for example, a general purpose solvent-based adhesive which is both waterproof and flexible is formed. Cellulose esterification leads to materials such as cellulose acetate [9004-35-7], which has been used as a pressure-sensitive adhesive tape backing. Cellulose can also be ethoxylated, providing hydroxyethylceUulose which is useful as a thickening agent for poly(vinyl acetate) emulsion adhesives. Etherification leads to materials such as methylceUulose [9004-67-5] which are soluble in water and can be modified with glyceral [56-81-5] to produce adhesives used as wallpaper paste (see Cellulose esters Cellulose ethers). 

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Chemical Properties. Neopentyl glycol can undergo typical glycol reactions such as esterification (qv), etherification, condensation, and oxidation. When basic kinetic studies of the esterification rate were carried out for neopentyl glycol, the absolute esterification rate of neopentyl glycol with / -butyric acid was approximately 20 times that of ethylene glycol with / -butyric acid (7). 

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Etherification. Many of the mono alkylphenols and some of the dialkylphenols are converted into ethoxylates which find commercial apphcation as nonionic surfactants (9). For example, -nonylphenol reacts with ethylene oxide under mild basic conditions. 

Etherification. Ethers of amyl alcohols have been prepared by reaction with ben2hydrol (63), activated aromatic haUdes (64), dehydration-addition reactions (65), addition to olefins (66—71), alkoxylation with olefin oxides (72,73) and displacement reactions involving thek alkah metal salts (74—76). 

Etherification. Isopropyl alcohol can be dehydrated ia either the Hquid phase over acidic catalysts, eg, sulfuric acid, or ia the vapor phase over acidic aluminas to give diisopropyl ether (DIPE) and propylene (qv). 

Propylene oxide is a useful chemical intermediate. Additionally, it has found use for etherification of wood (qv) to provide dimensional stabiUty (255,256), for purification of mixtures of organosiUcon compounds (257), for disinfection of cmde oil and petroleum products (258), for steriliza tion of medical equipment and disinfection of foods (259,260), and for stabilization of halogenated organics (261—263). 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

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). 

Reaction of olefin oxides (epoxides) to produce poly(oxyalkylene) ether derivatives is the etherification of polyols of greatest commercial importance. Epoxides used include ethylene oxide, propylene oxide, and epichl orohydrin. The products of oxyalkylation have the same number of hydroxyl groups per mole as the starting polyol. Examples include the poly(oxypropylene) ethers of sorbitol (130) and lactitol (131), usually formed in the presence of an alkaline catalyst such as potassium hydroxide. Reaction of epichl orohydrin and isosorbide leads to the bisglycidyl ether (132). A polysubstituted carboxyethyl ether of mannitol has been obtained by the interaction of mannitol with acrylonitrile followed by hydrolysis of the intermediate cyanoethyl ether (133). 

Because vanillin is a phenol aldehyde, it is stable to autooxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxy group and by aldol condensation at the aldehyde group. AH three functional groups in vanillin are... 

Etherification. Ethers of poly(vinyl alcohol) are easily formed. Insoluble internal ethers are formed by the elimination of water, a reaction cataly2ed by mineral acids and alkaU. 

Methyl tert-Butyl Ether (MTBE). Methyl tert-hutyi ether [1634-04-4] is made by the etherification of isobutylane with methanol, and there are six commercially proven technologies available. These technologies have been developed by Arco, IFF, CDTECH, Phillips, Snamprogetti, and Hbls (hcensed jointly with UOP). The catalyst in all cases is an acidic ion-exchange resin. The United States has been showing considerable interest in this product. Western Europe has been manufacturing it since 1973 (ANIC in Italy and Huls in Germany). Production of MTBE in Western Europe exceeded 600,000 tons in 1990. 

The various sources of isobutylene are C streams from fluid catalytic crackers, olefin steam crackers, isobutane dehydrogenation units, and isobutylene produced by Arco as a coproduct with propylene oxide. Isobutylene concentrations (weight basis) are 12 to 15% from fluid catalytic crackers, 45% from olefin steam crackers, 45 to 55% from isobutane dehydrogenation, and high purity isobutylene coproduced with propylene oxide. The etherification unit should be designed for the specific feedstock that will be processed. 

Etherification. Carbohydrates are involved in ether formation, both intramoleculady and intermoleculady (1,13). The cycHc ether, 1,4-sorbitan, an 1,4-anhydroalditol, has already been mentioned. 3,6-Anhydro-a-D-galactopyranosyl units are principal monomer units of the carrageenans. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers of cellulose (qv) are all commercial materials. The principal starch ethers are the hydroxyethyl and hydroxypropylethers (see Cellulose ethers Starch). 

Every polysaccharide contains glycosyl units with unsubstituted hydroxyl groups available for esterification or etherification. Polysaccharide derivatives are described by their degree of substitution (DS), which is the average number of substituent groups per glycosyl unit. Because each monomeric unit of cellulose molecules has free hydroxyl groups at C-2, C-3, and C-6, the maximum DS for cellulose, and all polysaccharides composed exclusively of neutral hexosyl units, the majority of polysaccharides, is 3.0. 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Etherification. A mixture of ethylene chlorohydrin ia 30% aqueous NaOH may be added to phenol at 100—110°C to give 2-phenoxyethanol [122-99-6] ia 98% yield (39). A cationic starch ether is made by reaction of a chlorohydfin-quaternary ammonium compound such as... 

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 ... 

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