Carboxyl Chain length

SPCs of medium carboxylic chain lengths (C6-C8) are the most persistent surfactants and constitute more than 70% of the total SPC detected in water. In sediments, the longer-chain SPC (C9-C1 l) are the most abundant ones. The SPC metabolites are more evenly distributed in the water column than the parent LAS. 

In another work, series of carboxylates from C-IO to C-22 have been used to examine the effect of anions on fire retardancy of PMMA/MgAl and PS/MgAl nanocomposites [90]. All the carboxylate-modified LDHs are well dispersed in PMMA, whereas none of them is well dispersed in PS. Eigure 13.11 shows the plot of PHRR versus number of carbons in the modifiers for both PMMA and PS nanocomposites. There is a little dependence of PHRR on the length of the carboxylate for PMMA. The reduction in PHRR is between 49 and 58% for all of the carboxylate-modified LDHs at 10% LDH loading. However, the PHRR reduction of the PS system falls off as the carboxylate chain length increases 56%... 

Varying alkyl chain length Varying carboxylate chain length ... 

Strictly speaking the term fatty add is restricted to those carboxylic acids that occur naturally in triacylglyc erols Many chemists and biochemists however refer to all unbranched carboxylic acids irrespective of their origin and chain length as fatty acids... 

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. 

Equation 20 is the rate-controlling step. The reaction rate of the hydrophobes decreases in the order primary alcohols > phenols > carboxylic acids (84). With alkylphenols and carboxylates, buildup of polyadducts begins after the starting material has been completely converted to the monoadduct, reflecting the increased acid strengths of these hydrophobes over the alcohols. Polymerization continues until all ethylene oxide has reacted. Beyond formation of the monoadduct, reactivity is essentially independent of chain length. The effectiveness of ethoxylation catalysts increases with base strength. In practice, ratios of 0.005—0.05 1 mol of NaOH, KOH, or NaOCH to alcohol are frequendy used. 

The pify of the leaving group and the hydrophobe chain length can dramatically affect the efficiency of the perhydrolysis reaction. Additionally, the stmcture of the acid portion of the precursor can affect the yield and sensitivity of the reaction to pH. The mono-4-hydroxybenzenesulfonic acid ester of a-decylsuccinic acid (13) undergoes extremely efficient perhydrolysis at much lower pHs than other peracid precursors, eg, decanoyloxybenzene sulfonate (14). This may be because of the neighboring group participation of the adjacent carboxylate as shown in Table 2 (115). 

Nylon resins are made by numerous methods (53) ranging from ester amidation (54) to the Schotten-Baumann synthesis (55). The most commonly used method for making nylon-6,6 and related resins is the heat-induced condensation of monomeric salt complexes (56). In this process, stoichiometric amounts of diacid and diamine react in water to form salts. Water is removed and further heating converts the carboxylate functions to amide linkages. Chain lengths are controlled by small amounts of monofunctional reagents. The molten finished nylon resin can be dkectly extmded to pellets. 

PhCH20COCl, Na2C03, H20,0°, 30 min, 72% yield. Alpha-omega diamines can be protected somewhat selectively with this reagent at a pH between 3.5 and 4.5, but the selectivity decreases as the chain length increases [H2N(CH2) NH2, n = 2, 71% mono n = l, 29% mono]. Hindered amino acids are protected in DMSO (DMAP, TEA, heat, 47-82% yield). These conditions also convert a carboxylic acid to the benzyl ester. ... 

Long-chain fatty acids (LCFAs) are aliphatic compounds with a terminal carboxyl group and with a chain length greater than 12 carbon atoms (e.g., lauric acid). Very long-chain fatty acids are fatty acids with more than 18 carbon atoms (e.g., stearic acid). 

Alkanesulfonates are the petrochemically derived sulfur analogs of soaps, which are alkane carboxylates based on renewable resources. The main difference between alkanesulfonates and soaps is, however, that alkanesulfonates consist of a rather complex mixture of homologs with different carbon chain lengths and isomers with an almost statistical distribution of the functional group along the hydrophobic carbon chain (Fig. 1), whereas soap is a mixture of homologs of alkane 1-carboxylates with an even number of carbon atoms. 

The metabolism of cinnamate and w-phenylalkane carboxylates has been studied in Rhodopseudomonaspalustris (Elder et al. 1992), and for growth with the higher homologs additional CO2 was necessary. The key degradative reaction was ()-oxidation, for compounds with chain lengths of three, five, and seven carbon atoms, benzoate was formed and further metabolized, but for the even-numbered compounds with four, six, and eight carbon atoms phenylacetate was a terminal metabolite. 

H. Muller, C. P. Herold, S. von Tapavicza, M. Neuss, W. Zollner, and F. Burbach. Esters of medium chain length carboxylic acids as oil-phase components in invert drilling muds (Ester von Car-bonsauren mittlerer Kettenl ge als Bestandteil der Olphase in Invert-Bohrspiilschlammen). Patent EP 386636, 1990. 

Such esterifications and acetal formations are achieved through enzyme catalyses. However, such reactions are relatively rare in aqueous conditions chemically. This is because the reversed reactions, hydrolysis, are much more favorable entropically. Kobayashi and co-workers found that the same surfactant (DBSA) that can catalyze the ether formation in water (5.2 above) can also catalyze the esterification and acetal formations reactions in water.52 Thus, various alkanecarboxylic acids can be converted to the esters with alcohols under the DBSA-catalyzed conditions in water (Eq. 5.6). Carboxylic acid with a longer alkyl chain afforded the corresponding ester better than one with a shorter chain at equilibrium. Selective esterification between two carboxylic acids with different alkyl chain lengths is therefore possible. 

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