Hydroxyl groups in alcohols

One of the most useful ways of introducing fluorine into organic compounds is the placement of the hydroxyl group in alcohols hydroxy compounds, and carboxylic acids Methyl alcohol reacts with anhydrous hydrogen fluoride at 100 500 °C in the presence of aluminum fluoride [60, 61], zinc fluoride [62] chromium fluonde [63], or a mixture of aluminum and chromium fluondes [64] to give a 20-78% yield of fluoromethane Attempted fluorinations of higher alcohols by this method failed [60]... 

The use of diethyltrifluaromethylamine and A ,fV-dimethyl-a,a-difluoro-benzylamine as fluorrnating reagents to replace hydroxyl groups in alcohols and carboxylic acids has been examined These fluoroamines are fairly stable com... 

All these steps proceed to afford free or N -substituted crystalline cytidines 6 in high yields [11] (cf. the preparation of N (tetramethylene)cytidine 6b in 95.4% yield in Section 1.1.). This simple one-pot reaction is also very easy to perform on a technical scale, as are the subsequently discussed analogous silylation-aminations of purine nucleosides and other hydroxy-N-heterocycles (cf. Sections 4.2.4 and 4.2.5). The concept of silylation-activation while simultaneously protecting hydroxyl groups in alcohols, phenols, or phosphoric acids by silylation was subsequently rediscovered and appropriately termed transient protection [16-18]. 

The hydroxyl group in alcohol 122 is then oxidized. Deprotonation of this ketone with KHMDS (1 eq.), followed by the addition of Davis oxaziridine (see Chapter 4 for a-hydroxylation of ketones)28 (2 eq.) allows the stereo-controlled introduction of the C-10 oxygen from the less hindered enolate face, providing only the (i )-hydroxyketone 123. Subsequent reduction of 123 with excess LAH provides the tetra-ol 124. Treatment of this compound with imidazole and TBSC1 followed by PPTS and 2-methoxypropene provides in one operation the acetonide 125 with 91% yield (Scheme 7-37). 

Fig. 4 Substitution of the hydroxyl group in alcohols (a) via pre-activation and (b) via direct catalytic substitution...

Table 8 Optimization of reaction conditions for direct substitution of the hydroxyl group in alcohol...

Many physical and chemical properties of substances have been determined by GC. Characterization of complex materials such as asphalts, polymers, and catalysts have been performed. Carbon number and the placement of hydroxyl groups in alcohols as well as vapor pressures of numerous compounds (Table 11.5) have been determined by GC. 

The major limitation of GC is the requirement for heat stability and volatility of the sample. Obviously, compounds that decompose at elevated temperatures (below 250°C) cannot normally be subjected to GC analysis. Many compounds of biochemical interest are not volatile in the useful temperature range of GC (up to about 200-250°C). Such compounds can often be converted to volatile derivatives. Hydroxyl groups in alcohols, carbohydrates, and sterols are converted to derivatives by trimethylsilylation or acetylation. Amino groups can also be converted to volatile derivatives by acetylation and silylation. Fatty acids are transformed to methyl esters for GC analysis, as described in Experiment 6. 

The functional group of alcohols and phenols is the hydroxyl group. In alcohols, this group is connected to an aliphatic carbon, whereas in phenols, it is attached to an aromatic ring. 

Reaction of Alcohol and Hydrobromic Acid.—The third reaction which proves the presence of the hydroxyl group in alcohol is with the halogen binary acids. When hydrochloric, or better hydrobromic or hydriodic acid, acts upon hot alochol a partial decomposition of the alcohol takes place and the ethyl halide and water are formed... 

The hydroxyl group in alcohol can be replaced by a halogen atom by means of the halides of phosphorus. A reaction between alcohol and phosphorus trichloride takes place according to the equation,... 

As a result of the reaction the hydrogen in the hydroxyl group in alcohol is replaced by the acetyl group. If a diatomic alcohol is used two acetyl groups are introduced. The reaction is of great analytical value as by means of its use the number of hydroxyl groups present in a substance of unknown structure can be determined. 

Hydroxyl groups in alcohols and phenols Silylation BSA, BSTFA, BSTFA + TMCS, HMDS, MSTFA, MSTFA + TMCS Most often used derivatives Good thermal stability... 

In the lUPAC system, the hydroxyl group in alcohols is indicated by the ending -ol. In common names, the separate word alcohol is placed after the name of the alkyl group. The following examples illustrate the use of lUPAC rules, with common names given in parentheses. 

Nucleophilic Substitution of Alcohols. The use of alcohols as electrophiles instead of halides and acetate compounds is an ideal method to prevent waste salt formation (Fig. 5). However, cataljdic substitution of the hydroxyl group in alcohols is difficult due to their poor leaving ability, which requires equimolar or greater amounts of reagents. Recently, several homogeneous catalysts, such as NaAuCh, InCla, ZrCh, La, Yb, Sc, Hf triflate, BCCeFsls, BF3, and p-toluenesulfonic acid have been used for nucleophilic substitution reactions of alcohols with amides (33), 1,3-dicarbonyl compounds (34), and allylsilanes (35). However, these catalysts are often limited by low catalytic activity and selectivity, can be difficult to reuse, and require the use of halogenated solvents. 

Replacement of hydroxyl groups in alcohols is typically carried out using anhydrous or concentrated aqueous solutions of hydrogen halides, phosphorus halides, thionyl chloride (SOCI2), or thionyl bromide ... 

One of the useful applications of NMR has been in the determination of functional groups, such as hydroxyl groups in alcohols and phenols, aldehydes, carboxylic acids, olefins, acetylenic hydrogens, amines, and amides. Relative errors in the range of 1 % to 5% arc reported. 

Some common functional groups include the hydroxyl group in alcohols, the carbonyl group in aldehydes and ketones, and a nitrogen atom in amines. 

Villamanan, M. A. Casanova, C. Roux, A. H. Grolier, J.-P. E. Calorimetric investigation of the interaction between oxygen and hydroxyl groups in (alcohol -t ether) at 298.15 K J. Chenu Thermodyn. 1982,14,251-258... 

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