Methylene and oxygen

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

The basic structure shared by most 3-sympatholytics is the side chain of 3-sympathomimetics (cf isoproterenol with the p-blockers propranolol, pindolol, atenolol). As a rule, this basic structure is linked to an aromatic nucleus by a methylene and oxygen bridge. The side chain C-atom bearing the hydroxyl group forms the chiral center. With some exceptions (e.g., timolol, penbuto-lol), all p-sympatholytics are brought as racemates into the market (p. 62). 

The Tg is related to chain stiffness and the geometry of the polymer chain. Flexible polymers with methylene and oxygen atoms in the chain, such as polyethylene, polyoxymethylene, and polysiloxane (silicone), have relatively low Tg values. The Tg of polyoxymethylene is somewhat higher than would be anticipated because of the dipole character of the C—O—C group, which increases the intermolecular forces and restricts segmental motion. 

Recent progress made in methylene and oxygen - atom chemistry has greatly extended our knowledge of atomic and free radical reactions and brought to light many similarities in the chemical behavior of these species. 

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

Environmental Impact. The volume of waste remover from these products is remarkably increased when compared to methylene chloride, petroleum, and oxygenate removers, since both /V-methy1pyrro1idinone and dibasic esters have low vapor pressures. Recovery of the remover after use is difficult because the finish is tesolubili2ed by the remover. A representative dibasic ester formula appears below for a thickened water rinse finish remover. 

Chloroform can be manufactured from a number of starting materials. Methane, methyl chloride, or methylene chloride can be further chlorinated to chloroform, or carbon tetrachloride can be reduced, ie, hydrodechlorinated, to chloroform. Methane can be oxychlorinated with HCl and oxygen to form a mixture of chlorinated methanes. Many compounds containing either the acetyl (CH CO) or CH2CH(OH) group yield chloroform on reaction with chlorine and alkali or hypochlorite. Methyl chloride chlorination is now the most common commercial method of producing chloroform. Many years ago chloroform was almost exclusively produced from acetone or ethyl alcohol by reaction with chlorine and alkali. 

Oxychlorination of Hydrocarbons. Methane was oxychlorinated with HCl and oxygen over a 4 3 3 CuCl—CUCI2—KCl molten mixture to give a mixture of chlorinated methanes, 60 mol % of which was carbon tetrachloride (28). Aqueous 20% HCl was used in the multistep process as the source of the acid. Anhydrous HCl is more typically used. Other oxychlorination processes can be made to yield high percentages of carbon tetrachloride starting from any of several hydrocarbon feeds (29—31). The typical reaction temperature is 400—600°C (see Chlorocarbons and chlorohydrocarbons. Methyl cm oRiDE Methylene cphoride and Cphoroform). 

Synthesis. These macrocycles are prepared from seven-membered ring dinitrile complexes, 84a-84c (Scheme 17), which contain either methylene, sulfur or oxygen in the five position (129). These cyclic dinitriles are synthesized by alkylating maleonitrile dithiolate or derivatives thereof with the corresponding dihalide. The dinitriles 84a-84c can be cyclized in magnesium propoxide to form porphyrazines 85a (33%), 85b (19%), and 85c (27%) (Scheme 17), which can be demetalated with trifluoroacetic to form 86a-86c. Additionally, 86a has been remetalated with nickel (87a, 92%), copper (88a, 95%), and zinc (89a, 94%). The sulfur and oxygen derivatives 85b, 85c, 86b, and 86c are of low solubility and are not suitable for further manipulation. 

There is a striking similarity in the behavior attributed to the triplet biradicals believed to be formed in the reactions of both triplet methylene and triplet oxygen with the 2-butenes. It should also be pointed out that in the triplet addition reactions of methylene, cis and trans olefins do not give the same cis and trans product ratios, indicating that the rate of spin inversion necessary for closure in the biradical intermediate occurs at a rate comparable to the rate of rotation about C—C bonds. 

---