Carbon and aromatic

Phosphabenzene, the phosphorus analogue of pyridine, is a species that, as with the methylenephosphines, formally contains a doubly coordinated phosphorus singly bound to one carbon and doubly bound to another. The first isolation of a phosphabenzene derivative was reported in 1966 using the reaction as shown below (equation 10). The parent phosphabenzene molecule was first isolated by the reaction (equation 11) of phosphorus tribromide with a staimane derivative, albeit in low yield.Further spectroscopic investigation of this parent molecule indicated it to be planar with indications of multiple bond character between phosphoms and carbon and aromatic delocalization. ... 

One effective technique for selective reaction is to employ one ester which possesses no a-hydrogen atoms. Simple aliphatic esters such as ethyl formate, diethyl oxalate and diethyl carbonate are commonly used while, among the aromatic esters, benzoic, substituted benzoic and furoic esters are commonly employed. Self-condensation of the ester providing the carbanion is not a major problem. Examples of this reaction are given in Scheme 4 further examples are listed in the reviews. Diethyl oxalate and ethyl formate react readily in this way, although forcing conditions are often necessary with diethyl carbonate and aromatic esters. 

A tandem strategy for indole annulation has been developed from indolylborates. Initial b-annulation was effected by the following sequence hydroboration of a terminally imsaturated allylic acetate with 9-BBN, reaction with 2-lithio-l-methylindole to nerate the borate palladium-induced cyclization at C-3, migration from boron to carbon and aromatization (Scheme 49) <91CC1219>. A development of this uses the hydroboration derivative (156) of a 1-alkenylindole, followed by... 

Important fiber materials are surface-treated glass, boron, graphite (carbon), and aromatic polyaramides (eg, DuPont s Kevlar). In most composites the reinforcement constitutes ca 65% of the final mass. Orientation of the fibers is important in establishing the properties of the laminate. Unidirectional, bidirectional, and random orientations are possible. The characteristics of the cured resin system are extremely important since it must transmit the applied stresses to each fiber. A critical region in a composite is the resin-fiber interface. The adhesive properties of epoxy resins make them especially suited for composite applications. 

The hydrocarbon family includes alkanes (single covalent bonds), alkenes (double bonds), alkynes (triple bonds), cycloalkanes (contain a ring or cycle of carbons), and aromatics (contain at least one highly unsaturated six-carbon ring). 

Table 23.6. Electrochemically active species on carbon and aromatic compounds [98]. (Reprinted from Carbon, 11(4), Kinoshita K, Bett JAS, Potentiodynamic analysis of surface oxides on carbon blacks, 403-11, 1973, with permission from Elsevier.)...

With the accumulation of results obtained from various and complex analyses of narrow cuts (Waterman method), correlations have been found f ctween refractive index, specific gravity and molecular weight on one hand, and percentages of paraffinic, naphthenic and aromatic carbon on the other. 

In order for the transferability of parameters to be a good description of the molecule, force fields use atom types. This means that a sp carbon will be described by different parameters than a. sp - carbon, and so on. Usually, atoms in aromatic rings are treated differently from sp atoms. Some force fields even parameterize atoms for specific functional groups. For example, the carbonyl oxygen in a carboxylic acid may be described by different parameters than the carbonyl oxygen in a ketone. 

Kinetic studies of nitration using dilute solutions of dinitrogen pentoxide in organic solvents, chiefly carbon tetrachloride, have provided evidence for the operation, under certain circumstances of the molecular species as the electrophile. The reactions of benzene and toluene were inconveniently fast, and therefore a series of halogenobenzenes and aromatic esters was examined. 

Formic acid is a good reducing agent in the presence of Pd on carbon as a catalyst. Aromatic nitro compounds are reduced to aniline with formic acid[100]. Selective reduction of one nitro group in 2,4-dinitrotoluene (112) with triethylammonium formate is possible[101]. o-Nitroacetophenone (113) is first reduced to o-aminoacetophenone, then to o-ethylaniline when an excess of formate is used[102]. Ammonium and potassium formate are also used for the reduction of aliphatic and aromatic nitro compounds. Pd on carbon is a good catalyst[103,104]. NaBH4 is also used for the Pd-catalyzed reduction of nitro compounds 105]. However, the ,/)-unsaturated nitroalkene 114 is partially reduced to the oxime 115 with ammonium formate[106]... 

Pure adiponitrile is a colorless Hquid and has no distinctive odor some properties are shown in Table 5. It is soluble in methanol, ethanol, chloroalkanes, and aromatics but has low solubiUty in carbon disulfide, ethyl ether, and aUphatic hydrocarbons. At 20°C, the solubiUty of adiponitrile in water is ca 8 wt % the solubiUty increases to 35 wt % at 100°C. At 20°C, adiponitrile dissolves ca 5 wt % water. 

Trichloroacetic acid K = 0.2159) is as strong an acid as hydrochloric acid. Esters and amides are readily formed. Trichloroacetic acid undergoes decarboxylation when heated with caustic or amines to yield chloroform. The decomposition of trichloroacetic acid in acetone with a variety of aUphatic and aromatic amines has been studied (37). As with dichloroacetic acid, trichloroacetic acid can be converted to chloroacetic acid by the action of hydrogen and palladium on carbon (17). 

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

In Group 14 (IV), carbon serves as a Lewis base in a few of its compounds. In general, saturated ahphatic and aromatic hydrocarbons are stable in the presence of BF, whereas unsaturated ahphatic hydrocarbons, such as propjdene or acetylene, are polymerized. However, some hydrocarbons and their derivatives have been reported to form adducts with BF. Typical examples of adducts with unsaturated hydrocarbons are 1 1 adducts with tetracene and 3,4-benzopyrene (39), and 1 2 BF adducts with a-carotene and lycopene (40). 

Dowtherm J is a mixture of isomers of an alkylated aromatic that contains only carbon and hydrogen. Dowtherm J can be used in Hquid-phase systems at temperatures as low as —73° C and in vapor-phase systems at temperatures from 185 to 315°C. Dowtherm Q is a mixture of diphenylethane and alkylated aromatics intended for Hquid-phase systems. It can be used at temperatures as low as —34°C. Dowtherm HT is a mixture of hydrogenated terphenyls intended for Hquid-phase systems. Dowtherm HT and Therminol 66 are essentially identical. 

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

Polymerization and GycliZation. Acetylene polymerizes at elevated temperatures and pressures which do not exceed the explosive decomposition point. Beyond this point, acetylene explosively decomposes to carbon and hydrogen. At 600—700°C and atmospheric pressure, benzene and other aromatics are formed from acetylene on heavy-metal catalysts. 

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