Alkane acidity

Table 4. Some geometrical features of the alkane/acid site transition states for protoly tic cracking. (a) cleavage on the primary C-C bond (b) cleavage on the secondary C-C bond.

We believe much more work is needed before ihe true nature of species obtained via the acid catalyzed treatment of haloalkanes is well understood and we are loathe to extrapolate from alkane/acid systems to those involving carbon halogen bonds. 

These materials are used industrially mainly in the reaction of hydration of alkanes (acid catalysis) and in the synthesis of methacrolein or isobutyric acid (redox catalysis). Because of the considerable number of available polyanion structures, it is possible to vary their acidic and redox properties according to the needs of a specific application. 

Figure 9 Classification of an aerosol sample (PM2.5, Augsburg ) (S/N, 100 1) with n-alkanes (orange), alkenes and cycloalkanes (light green), n-alkane acids (purple), partially hydrated naphthalenes and alkenyl-substituted benzenes (light blue), naphthalene and alkyl-substituted naphthalenes (yellow), polar benzenes (red), and alkyl-substituted benzenes (dark green). Bubbles with more than one colour have been identified by the scripts as belonging to more than one class [38],...

The branching ratios found for the decomposition of the five-coordinate anions provide a kinetic method for estimating alkane acidities. In principle this method can be applied... 

The overall order of alkane acidities deduced from the decomposition of silicon anions is the same as that obtained from the decomposition of alkoxides " " . The ethyl anion has the highest proton affinity, i.e., ethane is the weakest acid. The acidities of propane (secondary hydrogen) and of cyclobutane are both lower than that of methane, but all other alkanes are more acidic. The acidity of methane is particularly enhanced by a cyclopropyl substituent and by a t-butyl group. 

Before 1965, only a few poly-co-amino alkane acids have been reported. Let us mention Imoto etal [58] who described the polycondensation of /-menthone lactam (or 4-methyl-7-isopropyl-2-oxohexamethyleneimine) (XXVII), in presence of potassium or lithium as catalyst. The molecular weight of the polymer was very low because of the severe sterical hindrance of the side chain. 

Hydroxymethylsilanes have been prepared by oxidizing the a-silyl-a-boryl-methane, whereas ketones yield vinylboronates. Sodium silylalkane sulphonates result from [MegSiCCHajnjsAl and SO3, followed by hydrolysis, but Mc3Si-(CHajaAlCla and a,co-alkane acid chlorides give the diones (CHa)ntCO(CHa)8-SiMesL (n=4, 8). ... 

Sephadex A trade name for an insoluble hydrophilic substance prepared by cross-linking dextran, and used in gel filtration. It can also be linked to acidic or basic groups for ion exchange or to alkanes for the chromatography of lipophilic compounds. 

Laibinis P E, Flickman J J, Wrighton M S and Whitesides G M 1989 Orthogonal self-assembled monolayers— alkanethiols on gold and alkane carboxylic-acids on alumina Science 245 845-7... 

Alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Conventional paraffin-olefin (alkane-alkene) alkylation is an acid-catalyzed reaction, such as combining isobutylene and isobutane to isooctane. 

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

Acid-catalyzed isomerization reactions of alkanes as well as alkylation and condensation reactions are initiated by protolytic ionization. Available evidence indicates nonlinear but not necessarily triangular... 

Apart from Bronsted acid activation, the acetyl cation (and other acyl ions) can also be activated by Lewis acids. Although the 1 1 CH3COX-AIX3 Friedel-Crafts complex is inactive for the isomerization of alkanes, a system with two (or more) equivalents of AIX3 was fonnd by Volpin to be extremely reactive, also bringing abont other electrophilic reactions. 

The selection of solvents for quantitative work is not easy. Nitro-alkanes are sufficiently inert, but nitronium tetrafluoroborate is poorly soluble in them c. 0-3 %). Nitronium salts react rapidly with acetic anhydride, and less rapidly with acetic acid, A, A -dimethylformamide and acetonitrile, although the latter solvent can be used for nitration at low temperatures. Sulpholan was selected as the most suitable solvent ... 

Although it is not a reaction of alkenes, oxidation of some alkanes with Pd(ll) is cited here. 1-Adamantyl Irilluoroacetate (155) was obtained in above 50% yield by the reaction of adamantane with Pd(OAc)2 in trifluoroa-cetic acid at 80 C[171]. 

Although essentially inert m acid-base reactions alkanes do participate m oxidation-reduction reactions as the compound that undergoes oxidation Burning m air (combus tion) IS the best known and most important example Combustion of hydrocarbons is exothermic and gives carbon dioxide and water as the products... 

The carbon m methane has the lowest oxidation number (—4) of any of the com pounds m Table 2 4 Methane contains carbon m its most reduced form Carbon dioxide and carbonic acid have the highest oxidation numbers (+4) for carbon corresponding to Its most oxidized state When methane or any alkane undergoes combustion to form carbon dioxide carbon is oxidized and oxygen is reduced A useful generalization from Table 2 4 is the following... 

The C—H bonds of hydrocarbons show little tendency to ionize and alkanes alkenes and alkynes are all very weak acids The acid dissociation constant for methane for exam pie IS too small to be measured directly but is estimated to be about 10 ° (pK 60)... 

Acetylene and terminal alkynes are more acidic than other hydrocarbons They have s of approximately 26 compared with about 45 for alkenes and about 60 for alkanes Sodium amide is a strong enough base to remove a proton from acetylene or a terminal alkyne but sodium hydroxide is not... 

This proton is far more acidic than a hydrogen in an alkane... 

Systematic names for carboxylic acids are derived by counting the number of car bons m the longest continuous chain that includes the carboxyl group and replacing the e ending of the corresponding alkane by oic acid The first three acids m Table 19 1 methanoic (1 carbon) ethanoic (2 carbons) and octadecanoic acid (18 carbons) illus trate this point When substituents are present their locations are identified by number... 

Compounds with two carboxyl groups as illustrated by entries 10 through 12 are distinguished by the suffix dioic acid or dicarboxylic acid as appropnafe The final e m fhe base name of fhe alkane is refamed... 

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