Alcohols and ethers

Although cyclic terpene alcohols occur widely in nature, few have the physiological properties that make them important fragrance or flavor materials. Exceptions are a-terpineol and (—)-menthol, the latter because of its cooling/refreshing effect. Of the bicyclic monoterpene alcohols, bomeol deserves mention. 

Many cyclic sesquiterpene alcohols are key odor components in essential oils, for example, cedrol in cedarwood oil, the vetiverols in vetiver oil, and the santalols in sandalwood oil. Since these alcohols have not yet been synthesized on an industrial scale, they are described under the oil in which they occur (Chapter 3). Some of their derivatives, however, are discussed in this section. 

C10H20O, Mr 156.27, has three asymmetric carbon atoms in its cyclohexane ring and, therefore, occurs as four pairs of optical isomers. The configuration of four of these isomers is given above the other four are their mirror images. 

Physical Properties. The eight optically active menthols differ in their organoleptic properties [77]. (-)-Menthol has a characteristic peppermint odor and also exerts a cooling effect. The other isomers do not possess this cooling effect and are, therefore, not considered to be refreshing. ( )-Menthol occupies an intermediate position the cooling effect of the (-)-menthol present is distinctly perceptible. 

The enantiomeric menthols have identical physical properties (apart from their specific rotation), but the racemates differ from the optically active forms in, for example, their melting points. Although the differences between the boiling points of the stereoisomers are small, the racemates can be separated by fractional distillation. Boiling points (in °C at 101.3 kPa) are as follows  

14 Identify the structural formulas of the functional groups that distinguish alcohols and ethers. 

15 Given the molecular structures of alcohols or ethers, or information from which they may be obtained, predict relative values of boiling points or solubility in water. 

16 Given the name (or structural diagram) of an alcohol or ether, write the structural diagram (or name). 

17 Given the reactants (or products) of a dehydration reaction between two alcohols, predict the products (or reactants) of the reaction. 

Although the unshared electron pairs are not shown on the oxygen atoms In these Lewis diagrams, they play a key role In governing the physical and chemical properties of alcohols and ethers. 

On the more practical side, vast quantities of simple alcohols—methanol, ethanol, 2-propanol, 1-butanol—and many ethers are made from petroleum-derived hydrocarbons. These alcohols are widely used as solvents and as intermediates for the synthesis of more complex substances. 

Before turning to the specific chemistry of alcohols and ethers, we remind you that the naming of these compounds is summarized in Sections 7-2 and 7-3. The special problems encountered in naming cyclic ethers are discussed in Section 15-11A. 

Exercise 15-1 a. Draw the structure of 4-methoxy-1-penten-3-ol. b. Name the following structure by the IUPAC system  

Acetals seldom are usually hydrogenolyzed so readily under mild conditions. However, Howard and Brown, Jr. found that acetals may be hydrogenolyzed to give the corresponding ethers and alcohols over rhodium catalyst in the presence of acid. Acetals of secondary alcohols react faster than those of primary alcohols (eq. 13.1).8 

Palladium was about half as active as rhodium, and platinum and ruthenium were almost inactive for the hydrogenation of isopropenyl methyl ether. Since these metals showed the same order of activity for the hydrogenolysis of acetone diisopropyl acetal, it has been suggested that the dissociation of the acetal to unsaturated ether and alcohol to form an equilibrium mixture (eq. 13.2) constitutes the first step in the hydrogenolysis of acetals. Hydrogenation then removes the unsaturated ether and allows further conversion of the acetal to the unsaturated ether. 

This mechanism was supported by the experimental facts that the acetals of primary alcohols were less completely converted than those of secondary alcohols, because the equilibrium shown in eq. 13.2 will be less favorable for the formation of unsaturated ether when the alkoxy groups are primary. Acetals may also be hydrogenolyzed in a neutral solvent over a palladium catalyst not containing alkali.9,10 

Lipkowitz et al. observed that the hydrogenation of cyclic enol ether 1 to 2 over a 10% Pd-C in ethanol was accompanied by the formation of bicyclic acetals of the formula 3, of which the endo isomer was hydrogenolyzed to give 2 much more rapidly 

Alkoxytrimethylsilanes such as the ethoxy, isopropoxy, and f-butoxysilanes were also hydrogenolyzed under the same conditions, although the reaction could not be monitored by hydrogen uptake when the hydrocarbon products were gaseous. Ary-loxytrimethylsilanes, such as 4-(trimethylsilyl)phenoxytrimethylsilane, were hydrogenated to the corresponding cyclohexyloxy derivatives over Raney Ni at elevated temperature and pressure the Ar-OSi bond remained intact. 

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Outside of hydrocarbons, certain organic oxygenated compounds such as the alcohols and ethers are henceforth utilized in the formulation of gasolines. These are mostly methanol, ethanol, propanols and butanols, as well as methyl and ethyl ethers obtained from and Cj olefins ... 

Additional gas-phase reactivity data, such as gas-phase acidities of alcohols [41], proton affinities of alcohols and ethers [41], and proton affinities of carbonyl compounds [42] could equally well be described by similar equations. 

Homologous mono-alkyl ethers of ethylene glycol, such as monoethyl glycol (or 2-ethoxyethanol), HOC2H4OC2H5, form excellent solvents as they combine to a large extent the solvent properties of alcohols and ethers. The monoethyl and the monomethyl members have the technical names of ethyl cellosolve and methyl cellosolve respectively. Dioxan... 

Cold concentrated sulphuric acid will remove unsaturated hydrocarbons present in saturated hydrocarbons, or alcohols and ethers present in alkyl halides. In the former case soluble sulphonated products are formed, whilst in the latter case alkyl hydrogen sulphates or addition complexes, that are soluble in the concentrated acid, are produced. 

It is marketed as a 35-40 per cent, solution in water (formalin). The rpactions of formaldehyde are partly typical of aldehydes and partly peculiar to itself. By evaporating an aqueous solution paraformaldehyde or paraform (CHjO), an amorphous white solid is produced it is insoluble in most solvents. When formaldehyde is distilled from a 60 per cent, solution containing 2 per cent, of sulphuric acid, it pol5unerises to a crystalline trimeride, trioxane, which can be extracted with methylene chloride this is crystalline (m.p. 62°, b.p. 115°), readily soluble in water, alcohol and ether, and devoid of aldehydic properties ... 

The monoalkyl ethers with R = CHj, CjHj and C4H, , known respectively as methyl ceUoaolve, ceUosolve and hutyl cellosolve, are of great commercial value, particularly as solvents, since they combine the properties of alcohols and ethers and are miscible with water. Equally important compounds are the carbitols (monoalkyl ethers of diethyleneglycol) prepared by the action of ethylene oxide upon the monoethers of ethylene glycol ... 

Most polysaccharides are insoluble or sparingly soluble in cold water, insoluble in cold alcohol and ether, and rarely possess melting points. Only inuUn melts at about 178° (dec.) after drying at 130°. 

It is convenient to consider the indiflferent or neutral oxygen derivatives of the hydrocarbons—(a) aldehydes and kelones, (b) esters and anhydrides, (c) alcohols and ethers—together. All of these, with the exception of the water-soluble members of low molecular weight, are soluble only in concentrated sulphuric acid, i.e., fall into Solubility Group V. The above classes of compounds must be tested for in the order in which they are listed, otherwise erroneous conclusions may be drawn from the reactions for functional groups about to be described. 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

Dichloroacetic acid [79-43-6] (CI2CHCOOH), mol wt 128.94, C2H2CI2O2, is a reactive intermediate in organic synthesis. Physical properties are mp 13.9°C, bp 194°C, density 1.5634 g/mL, and refractive index 1.4658, both at 20°C. The Hquid is totally miscible in water, ethyl alcohol, and ether. Dichloroacetic acid K = 5.14 X 10 ) is a stronger acid than chloroacetic acid. Most chemical reactions are similar to those of chloroacetic acid, although both chlorine... 

Alcohols and Ethers Blended with Gasoline, Pub. 4261, American Petroleum Institute, Washington, D.C., Chapt. 4, pp. 23—27. 

Aldehydes fiad the most widespread use as chemical iatermediates. The production of acetaldehyde, propionaldehyde, and butyraldehyde as precursors of the corresponding alcohols and acids are examples. The aldehydes of low molecular weight are also condensed in an aldol reaction to form derivatives which are important intermediates for the plasticizer industry (see Plasticizers). As mentioned earlier, 2-ethylhexanol, produced from butyraldehyde, is used in the manufacture of di(2-ethylhexyl) phthalate [117-87-7]. Aldehydes are also used as intermediates for the manufacture of solvents (alcohols and ethers), resins, and dyes. Isobutyraldehyde is used as an intermediate for production of primary solvents and mbber antioxidants (see Antioxidaisits). Fatty aldehydes Cg—used in nearly all perfume types and aromas (see Perfumes). Polymers and copolymers of aldehydes exist and are of commercial significance. 

In acetic acid solvent, ethylene gives 1,3-propanediol acetates (46) and propylene gives 1,3-butanediol acetates (47). A similar reaction readily occurs with olefinic alcohols and ethers, diolefins, and mercaptans (48). 

Iron(II) fluoride tetrahydrate [13940-89-17, Fep2 4H2O, is prepared by dissolving iron metal ia warm hydrofluoric acid and precipitating with ethanol. The stmcture of the soHd consists of discrete [FeF2(H20)4] octahedra ia which F and H2O are randomly distributed over the possible sites. The white sohd turns brown ia air and decomposes at 100°C. It is slightly soluble ia water, alcohol, and ether and is soluble ia dilute acid. 

Acetophenone. Acetophenone [98-86-2] (methyl phenyl ketone) is a colorless Hquid that forms laminar crystals at low temperature (mp 20°C). It has a characteristic sweet orange blossom odor, and is soluble in alcohols and ethers. It is found in nature in oil of casatoreum, obtained from beavers oil of labdanum, recovered from plants and in buds of balsam poplar. It can be prepared by the Friedel-Crafts reaction (qv) of acetyl chloride with benzene in the presence of aluminum chloride however, this route is of Htde commercial significance. 

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). 

Physical Properties. The physical properties of cyanoacetic acid [372-09-8] NM7—CH2COOH (28) ate summarized in Table 4. The industrially most important esters ate methyl cyanoacetate [105-34-0] and ethyl cyanoacetate [105-56-6]. Both esters ate miscible with alcohol and ether and immiscible with water. 

Dibydroxyaluminum monostearate, (HO)2Al(OOC(CH2) gCH2), is a fine white to yeUowish-white powder with a faint characteristic odor and low toxicity. This salt melts at 155°C and is insoluble in water, alcohol, and ether (31). It is prepared by treating an aqueous solution of... 

Monohydroxyaluminum distearate, (HO)Al(OOC(CH2) gCH2)2, used to be the largest selling aluminum carboxylate (1). Although stiU sold, the product is no longer Hsted in the U.S. International Trade Commission Report (1) because of low volume or confidentiahty constraints because of too few supphers. Aluminum distearate is a white powder that is insoluble in water, alcohol, and ether. A key property is its abiUty to gel vegetable oils and hydrocarbons. Aluminum distearate is prepared by the reaction of aqueous sodium stearate with aqueous aluminum sulfate or chloride at pH 7.3. Aluminum monostearate is formed if the sodium stearate solution is held at pH 9.5 (44). 

Uranium hexafluoride [7783-81-5], UF, is an extremely corrosive, colorless, crystalline soHd, which sublimes with ease at room temperature and atmospheric pressure. The complex can be obtained by multiple routes, ie, fluorination of UF [10049-14-6] with F2, oxidation of UF with O2, or fluorination of UO [1344-58-7] by F2. The hexafluoride is monomeric in nature having an octahedral geometry. UF is soluble in H2O, CCl and other chlorinated hydrocarbons, is insoluble in CS2, and decomposes in alcohols and ethers. The importance of UF in isotopic enrichment and the subsequent apphcations of uranium metal cannot be overstated. The U.S. government has approximately 500,000 t of UF stockpiled for enrichment or quick conversion into nuclear weapons had the need arisen (57). With the change in pohtical tides and the downsizing of the nation s nuclear arsenal, debates over releasing the stockpiles for use in the production of fuel for civiUan nuclear reactors continue. 

Nitrate. Cerium(III) nitrate hexahydrate [10294-41 -4] Ce(N03) 6H20, is a commercially available soluble salt of cerium, and because of ready decomposition to the oxide, it is used, for example, when a porous sohd is to be impregnated with cerium oxide. The nitrate is very soluble in water, up to about 65 wt %. It is also soluble in a wide range of polar organic solvents such as ketones, alcohols, and ethers. 

CeOCl. The anhydrous cerous chloride [7790-86-5] can be made from the hydrated salt by suppressing oxyhahde formation during thermal dehydration by the presence of hydrogen chloride or ammonium chloride. The anhydrous salt is soluble in a variety of organic solvents, eg, alcohols and ethers, has mp 817°C, and can be volatilized at high temperatures in vacuum. 

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