Carbon dioxide with triple bonds

Ammonium carbamates are readily and reversibly produced on reaction of secondary amines with carbon dioxide. In the presence of a ruthenium catalyst precursors such as Ru3(CO)12 [3], (arene)RuCl2(PR3) [4] or Ru(methallyl)2(dppe) [5] (dppe=bis(diphenylphosphino)ethane) complexes, the three-component combination of a secondary amine, a terminal alkyne, and carbon dioxide selectively provides vinylcarbamates resulting from addition of carbamate to the terminal carbon of the triple bond (Scheme 2). 

Also, a carbon atom can share two or three electrons with atoms other than carbon. Examples of this are the double bonds in carbon dioxide and the triple bond in hydrogen cyanide. 

Of course, in all cases each carbon has a full octet of electrons. Carbon also forms double and triple bonds with several other elements that can exhibit a covalence of two or three. The carbon-oxygen (or carbonyl) double bond appears in carbon dioxide and many important organic compounds such as methanal (formaldehyde) and ethanoic acid (acetic acid). Similarly, a carbon-nitrogen triple bond appears in methanenitrile (hydrogen cyanide) and eth-anenitrile (acetonitrile). 

When the nitrogen atom of a pyridine is sufficiently nucleophilic, for example 3-cyano- (pK 1.45) but not 3-bromopyridine (pATa 0.9), attack occurs at the triple bond of the ester.238 The reaction can be very vigorous and, if carried out at - 60° in ether, pyridine itself appears to yield the zwitterion 1 which can be trapped by carbon dioxide. No direct physical evidence has been obtained for 1 and the first product detectable by low-temperature NMR measurements is the 9a//-quinolizine 5.239 Both geometrical forms of the betaine (2) have been isolated, and, at 0° in chloroform, decomposition to carbon dioxide, detected by its absorption at 2335 cm-1, and a red tar, occur rapidly. Treatment of the betaines with aqueous perchloric acid at its freezing point, however,... 

Figure 7.12 outlines how hydantoin is produced during the synthesis of methionine depicted in Figure 7.11. Initially, the aminonitrile B is formed. With its amino group it adds to carbon dioxide, which—under the weakly basic reaction conditions—is followed by the formation of the carbamate ion D. In a fully analogous fashion, ammonia reacts with carbon dioxide to give ammonium carbamate (cf. Section 8.2). The intermediate D in Figure 7.12 permits the intramolecular and thus kinetically favored—i.e., fast—addition of the oxyanion to the C=N triple bond. The addition product is the negatively charged heterocycle F, which in...

B sp hybridization can be found at an atom that has formed a triple bond with a single bond or that has formed two double bonds. There are two double bonds found around the carbon atom in carbon dioxide. 

Stoichiometric reaction with oxygen to give carbon dioxide and water in their standard states was assumed. The data are summarized in the Experimental section. It can be seen that the experimental results agree well with calculated values showing that the triple bond was retained during polymerization. 

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... 

In general, the acetylenic triple bond is highly reactive toward hydrogenation, hydroboration, and hydration in the presence of acid catalyst. Protection of a triple bond in disubstituted acetylenic compounds is possible by complex formation with octacarbonyl dicobalt [Co2(CO)g Eq. (64) 163]. The cobalt complex that forms at ordinary temperatures is stable to reduction reactions (diborane, diimides, Grignards) and to high-temperature catalytic reactions with carbon dioxide. Regeneration of the triple bond is accomplished with ferric nitrate [164], ammonium ceric nitrate [165] or trimethylamine oxide [166]. 

Cyclic carbonyl ylides, formed from diazo amides or diazo anhydrides through intramolecular carbene addition to the carbonyl group, react with the triple bond of a dipolarophile to produce bicyclic adducts. The latter undergo a retrodiene reaction, splitting off an alkyl isocyanate or carbon dioxide to give furan derivatives. 

Double and Triple Bonds Sometimes an atom shares more than one electron with another atom. In the molecule carbon dioxide, shown in Figure 17, each of the oxygen atoms shares two electrons with the carbon atom. The carbon atom shares two of its electrons with each oxygen atom. When two pairs of electrons are involved in a covalent bond, the bond is called a double bond. Figure 17 also shows the sharing of three pairs of electrons between two nitrogen atoms in the nitrogen molecule. When three pairs of electrons are shared by two atoms, the bond is called a triple bond. 

The reaction of various 2-arylacetylenesulfonamides, isothiocyanates and potassium carbonate in acetone at 50-55°C gives 3-(alkylamino)(or anilino)-5-aryl-l,4,2-dithiazine 1,1-dioxides 6, which are the Michael adducts of intermediate potassium salts of 3-substituted l-(arylethynyl-sulfonyl)thioureas.8 In contrast to the reaction of styrenesulfonamides with isothiocyanates, the potassium salts cannot be isolated since they are very soluble in warm acetone and their triple bonds are more susceptible to nucleophilic attack. Aqueous 5 M sodium hydroxide may be used in place of potassium carbonate. 

Propiolic Acid, HC=C.COOH, is a liquid with a pungent odor resembling that of acetic acid. After freezing it melts at 9°. It can be distilled without decomposition only under diminished pressure. It is interesting on account of the fact that its reactions show clearly its relation to acetylene. It forms as an acid, well characterized salts, and as a triple bonded compound, metallic derivatives, which result from the replacement of the hydrogen atom joined to carbon by silver or copper. When the acid is treated with an ammoniacal solution of silver nitrate a colorless, crystalline salt is formed, which soon turns yellow and explodes when struck. Propiolic acid may be prepared by the action of carbon dioxide on the sodium derivative of acetylene —... 

To share a total of eight electrons with other atoms, a carbon atom may exhibit more than one type of bonding. The possibilities are the following (1) form four single bonds, as in methane, CH (2) form a double bond and two single bonds, as in formaldehyde, H CO (3) form two double bonds, as in carbon dioxide, CO or (4) form a triple bond and a single bond, as in hydrogen cyanide, HCN. 

SCHEME 2.11 Constructing molecules from atoms with multiple connectivities (a) Carbon dioxide (CO2) with double bonds, (b) Dinitrogen (N2) with a triple bond. 

That compound X has a peak near 3200 cm indicates that it has a terminal triple bond. The peak near 2100 cm Ms also associated with that triple bond. These facts surest that compound X is 1-hexyne, something that is confirmed by the results of its oxidation to a five-carbon carboxylic acid and carbon dioxide. 

In still other types of molecules, a central atom is surrounded by only two regions of electron density. Figure 1.10 shows Lewis structures and ball-and-stick models of carbon dioxide (CO2) and acetylene (C2H2). As with double bonds, VSEPR treats triple bonds as one region of electron density. 

A variation used the amine moiety of an amino-alkyne such as 1.167 rather than a Grignard regent. Condensation of the corresponding alkyne anion with carbon dioxide gave 4-(N,N-dimethylamino)but-2-ynoic acid, 1.168. Catalytic hydrogenation of the triple bond gave 4-(N,N-dimethylamino)but-2-enoic acid,... 

The yield of product from the carbon dioxide reaction with the alkyne anion was very poor, as it was with the vinyl Grignard derived from 1.166. Extending the carbon chain between the triple bond and the dimethylamino group, as in the reaction of 1.170 with sodium amide and then carbon dioxide, - however, led to... 

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