Alcohols, Phenols, Thiols, and Ethers

Alcohols are compounds of the general formula R-OH in which the hydroxyl group -OH is bonded to a saturated carbon atom. Three classes of alcohols can be distinguished  

Primary alcohol Secondary alcohol Tertiary alcohol 

Primary alcohols are the most common ones, and the most frequently used. They occur naturally in liquor, wine, beer, and in many natural essences of fruits and flowers. They are very important for the chemistry of fragrances and detergents. 

Several alcohols, and especially methyl alcohol and ethyl alcohol, are produced industrially in large quantities. 

At room temperature, none of them is gaseous. Primary alcohols are liquids up to Cu (undecyl alcohol) beyond, they are solids. Their boiling point is always higher than that of the homologous hydrocarbon having the same number of carbon atoms. As an example, ethane C2H6 boils at — 88.5 °C, while ethyl alcohol boils at +78.2 °C. 

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Name and draw structures of alcohols, phenols, ethers, thiols and sulfides. 

Disposal methods for some of the more common classes of organic compounds may be found in Chemical Safety Matters (hydrocarbons halogenated hydrocarbons alcohols and phenols ethers, thiols, and organosnlfnr componnds carboxylic acids and derivatives aldehydes ketones amines nitro and nitroso componnds and peroxides). 

For all of these related compounds (alcohols, enols, phenols, ethers, thiols, and thioethers), some properties of which are provided in Table 8.3, it might also be anticipated that the nonbonding electrons (Chapter 1) on oxygen or sulfur could participate in reactions occurring elsewhere in the organic framework, and, indeed, it is common to find that processes taking place remote to the heteroatom are also affected by its presence. 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Apart from complex formation involving metal ions (as discussed in Chapter 4), crown ethers have been shown to associate with a variety of both charged and uncharged guest molecules. Typical guests include ammonium salts, the guanidinium ion, diazonium salts, water, alcohols, amines, molecular halogens, substituted hydrazines, p-toluene sulfonic acid, phenols, thiols and nitriles. 

The nucleophilic addition of alcohols [130, 204-207], phenols [130], carboxylates [208], ammonia [130, 209], primary and secondary amines [41, 130, 205, 210, 211] and thiols [211-213] was used very early to convert several acceptor-substituted allenes 155 to products of type 158 and 159 (Scheme 7.25, Nu = OR, OAr, 02CR, NH2, NHR, NRR and SR). While the addition of alcohols, phenols and thiols is generally carried out in the presence of an auxiliary base, the reaction of allenyl ketones to give vinyl ethers of type 159 (Nu = OMe) is successful also by irradiation in pure methanol [214], Using widely varying reaction conditions, the addition of hydrogen halides (Nu= Cl, Br, I) to the allenes 155 leads to reaction products of type 158 [130, 215-220], Therefore, this transformation was also classified as a nucleophilic addition. Finally, the nucleophiles hydride (such as lithium aluminum hydride-aluminum trichloride) [211] and azide [221] could also be added to allenic esters to yield products of type 159. 

Dihydropyran is of value as a protecting group for alcohols and phenols, and to a lesser extent amines, carboxylic acids and thiols (B-67MI22403, B-81MI22404). The resulting tetrahydropyranyl ethers (736) are stable to base, but are readily cleaved under acidic conditions (Scheme 284). 

A mild procedure for the appendage of MOM groups to acid-sensitive substrates is illustrated by the protection of the allylic alcohol in Avermectin derivative 259.1 using [(methoxymethyl)thio]-2-pyridine (259 2) sitver(I) Inflate and sodium acetate in THF at room temperature [Scheme 4.259],479 Primary secondary and tertiary alcohols and phenols are methoxymethylated in good yield though phenols are slower to react. Reagent 259.2 (bp 66 °C/0.088 kPa) is easily prepared in 75% yield by the reaction of pyridine-2-thiol with dimethoxy-methane activated by trifluoroborane etherate. 

Cleavage of ethers. This combination cleaves methyl ethers of primary and secondary 2ilcohols readily. With the latter substrates, retention of configuration obtains. Aryl methyl ethers are cleaved very slowly by this method. Benzyl ethers of both alcohols and phenols are also cleaved and in high yield the former ethers are cleaved more readily. Presumably BFj coordinates with the ethereal oxygen to form n oxonium intermediate that is then attacked by the thiol (a soft nucleophile). ... 

The number of proposed methods for alcoholic and phenolic S-analog derivatization for GC analysis is significantly less than those for alcohols. The most objective reason for this is the lower frequency of their determinations in real analytical practice. In accordance with general recommendations, thiols and thio-phenols may be converted into TFA (PFP, HFB) esters or PFB ethers (5-TMS derivatives seems not as stable as G-TMS ethers). In addition to the optimization of chromatographic parameters, the derivatization of these compounds is necessary to prevent their oxidation by atmospheric oxygen. 

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