Acids Homologous series

Formic acid was first described by S. Fisher in 1670, who obtained it from the distillate of ants. The first nine members of the aliphatic carboxylic acids homologous series are liquids at room temperature. The first solid aliphatic carboxylic acid is decanoic acid, which has a melting point of 31.5°C. An unsaturated principal chain considerably lowers the melting point temperature. For example, c/s-oleic acid is a liquid at 5°C, and the cis and tram isomers have notably different melting temperatures. The tram isomer of oleic acid is eladic acid, which has a melting point of 44-45°C. The first three members of the aliphatic carboxylic acid homologous series are easy soluble in water. 

Spreading velocities v are on the order of 15-30 cm/sec on water [39], and v for a homologous series tends to vary linearly with the equilibrium film pressure, it", although in the case of alcohols a minimum seemed to be required for v to be appreciable. Also, as illustrated in Fig. IV-3, substrate water is entrained to some depth (0.5 mm in the case of oleic acid), a compensating counterflow being present at greater depths [40]. Related to this is the observation that v tends to vary inversely with substrate viscosity [41-43]. An analysis of the stress-strain situation led to the equation... 

The lower members of other homologous series of oxygen compounds— the acids, aldehydes, ketones, anhydrides, ethers and esters—have approximately the same limits of solubility as the alcohols and substitution and branching of the carbon chain has a similar influence. For the amines (primary, secondary and tertiary), the limit of solubility is about C whilst for the amides and nitriles it is about C4. 

One of the most sensitive tests of the dependence of chemical reactivity on the size of the reacting molecules is the comparison of the rates of reaction for compounds which are members of a homologous series with different chain lengths. Studies by Flory and others on the rates of esterification and saponification of esters were the first investigations conducted to clarify the dependence of reactivity on molecular size. The rate constants for these reactions are observed to converge quite rapidly to a constant value which is independent of molecular size, after an initial dependence on molecular size for small molecules. The effect is reminiscent of the discussion on the uniqueness of end groups in connection with Example 1.1. In the esterification of carboxylic acids, for example, the rate constants are different for acetic, propionic, and butyric acids, but constant for carboxyUc acids with 4-18 carbon atoms. This observation on nonpolymeric compounds has been generalized to apply to polymerization reactions as well. The latter are subject to several complications which are not involved in the study of simple model compounds, but when these complications are properly considered, the independence of reactivity on molecular size has been repeatedly verified. 

Formic acid [64-18-6] (methanoic acid) is the first member of the homologous series of alkyl carboxyHc acids. It occurs naturally ia the defensive secretions of a number of insects, particularly of ants. Although the acid nature of the vapors above ants nests had been known since at least 1488, the pure acid was not isolated until 1671, when the British chemist John Ray described the isolation of the pure acid by distillation of ants (1). This remained the main preparative method for more than a century until a convenient laboratory method was discovered by Gay-Lussac (2). The preparation of formates using carbon monoxide was described by Berthelot in 1856. 

Formic acid exhibits many of the typical chemical properties of the aHphatic carboxyHc acids, eg, esterification and amidation, but, as is common for the first member of an homologous series, there are distinctive differences in properties between formic acid and its higher homologues. The smaller inductive effect of hydrogen in comparison to an alkyl group leads, for example, to formic acid = 3.74) being a considerably stronger acid than acetic acid... 

Naphthenic acids are lepiesented by a general formula where n indicates the carbon number and specifies a homologous series. The ... 

As is not uncommon in homologous series, close homologues sometimes showed anomalous behaviour, e.g., of the benzilic acid esters with the following basic components —... 

Bornyl Propionate.—The propionic acid ester of borneol closely resembles the acetic ester, but as is, of course, usual in homologous series, its odour is slightly different. It has the formula... 

Where FCl is the solute gas-liquid partition coefficient, r is the tendency of the solvent to interact through k- and n-electron pairs (Lewis basicity), s the contribution from dipole-dipole and dipole-induced dipole interactions (in molecular solvents), a is the hydrogen bond basicity of the solvent, b is its hydrogen bond acidity and I is how well the solvent will separate members of a homologous series, with contributions from solvent cavity formation and dispersion interactions. 

The kinetics of reactions of bifunctional compounds are especially significant in relation to polymer reactions. The esterification rate constants shown in the third column (B) of Table V for the homologous series of dibasic acids do not differ greatly from those for the monobasic acids. These differences vanish as the length of chain separating the carboxyl groups increases. 

Lin, S. L., Inoue, Y., and Inoue S., Evaluation of high-performance anion-exchange chromatography with pulsed electrochemical and fluorometric detection for extensive application to the analysis of homologous series of oligo-and polysialic acids in bioactive molecules, Glycobiology, 9, 807, 1999. 

The major components have been identified tentatively as phenolic and fatty acids. At this time, seven phenolics have been identified in only four of the fractions. These are shown in Table III. A measure of the magnitude of the confidence level (cc) with a spectrum of standards is given. The first three entries are from the sunflower the last, from the Jerusalem artichoke. In all fractions isolated, both from the sunflower and the Jerusalem artichoke, a homologous series of fatty acids ranging from Cjo to Ci8 have been identified also by GC-MS. Even-chain, Cj6 to Cjs saturated and Cxs mono- and di-unsaturated, predominated. This is not surprising, since fatty acids are major constituents of plant... 

Figure 3. A homologous series of three tyrosine dipeptide derivatives gave rise to three new polyiminocarbonates that differed only in the length of the alkyl chain attached to the carboxylic acid group of the dipeptide.

The scheme of the most common hosts in this study (Fig. 40) shows that they can be considered as a homologous series of dicarboxylic acids of different chain length (1,2-, 1,4-, 1,6-, and 1,7-diacids, respectively) involving an essentially rigid central segment. A summary substantiates the similarity of the mean angles of /, 7, and 26 (Table 23) and a more or less steady shape of these host molecules in the free state... 

Their hydrophobicity and their plasticity were appreciated and used for a long time in a wide range of activities. To our knowledge, the first wax to have been exploited is beeswax. Beeswax is produced by various species of bees in the world, and it has a melting point between 62°C and 64°C. It mainly contains homologous series of even-numbered fatty acids (C22 C34, C2 being the predominat compound), odd-numbered ra-alkanes (C2i C33, C27 being the major compound) and even-numbered palmitic esters from C40 to C52 (Tulloch and Hoffman, 1972 Kolattukudy, 1976). Hydroxy esters, diesters and hydroxy diesters also form part of beeswax to a lesser extent. 

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