Carbon, acids hydrides

Some examples of alkylation reactions involving relatively acidic carbon acids are shown in Scheme 1.3. Entries 1 to 4 are typical examples using sodium ethoxide as the base. Entry 5 is similar, but employs sodium hydride as the base. The synthesis of diethyl cyclobutanedicarboxylate in Entry 6 illustrates ring formation by intramolecular alkylation reactions. Additional examples of intramolecular alkylation are considered in Section 1.2.5. Note also the stereoselectivity in Entry 7, where the existing branched substituent leads to a trans orientation of the methyl group. 

It is well known that strong electrophiles such as carbocations are reduced by organosilicon hydrides (Eq. 1).3,70,71 On the other hand, simple mixtures of organosilicon hydrides and compounds with weakly electrophilic carbon centers such as ketones and aldehydes are normally unreactive unless the electrophilicity of the carbon center is enhanced by complexation of the carbonyl oxygen with Brpnsted acids3,70 73 or certain Lewis acids (Eq. 2).1,70,71,74,75 Using these acids, hydride transfer from the silicon center to carbon may then occur to give either alcohol-related or hydrocarbon products. 

Buncel and Menon (1977) have studied reactions of potassium hydride solubilized in tetrahydrofuran by 18-crown-6 [3]. Very weak carbon acids such as triphenylmethane [ 151J (pAa = 31.5), diphenylmethane [152] (pAa = 33.1), and di-/j-tolylmethane [153] (pAa = 35.1) were completely metallated. After... 

When a nucleophile containing a heteroatom reacts at a carboxyl carbon SN, reactions occur that convert carboxylic acid derivatives into other carboxylic acid derivatives, or they convert carbonic acid derivatives into other carbonic acid derivatives. When an organometallic compound is used as the nucleophile, SN reactions at the carboxyl carbon make it possible to synthesize aldehydes (from derivatives of formic acid), ketones (from derivatives of higher carboxylic acids), or—starting from carbonic acid derivatives—carboxylic acid derivatives. Similarly, when using a hydride transfer agent as the nucleophile, SN reactions at a carboxyl carbon allow the conversion of carboxylic acid derivatives into aldehydes. 

The last analysis can also be employed to control Nos. I. and II. for if we represent the volume of nitrogen, contained in the original gas, by X, that of hydride of ethyl hyy, and that of olefiant gas by and further, the volume of mixed gases, oxygen consumed, and carbonic acid generated, respectively by A, B and C, we have the following equations —... 

The gas is therefore hydride of methyl (light carburetted hydrogen), 1 voL of which consumes 2 vols. oxygen and generates 1 vol. carbonic acid, and the specific gravity of which is -5528, numbers which correspond almost exactly with those obtained by experiment. 

By reaction with alkyl halides, esters of sulfonic and carbonic acids, trimethy-loxonium tetrafluoroborate, diazo compounds, Mannich or Mitsunobu conditions or miscellaneous reagents. Methyl iodide is a versatile and effective methylating reagent that can be used at room temperature, at moderate temperatures in a tightly closed vessel or at high temperatures in an autoclave. 2,4-Dihydropyrazol-3-one 1 was methylated at N1 with sodium hydride in boiling 1,4-dioxane followed by methyl iodide at room temperature. l,2-Dihydropyrazol-3-one 2 was obtained in 59% yield (79AP853) (Scheme 1). 

Carbon Dioxide, Carbonic acid gas carbonic an -hydride. COji mol wt 44.01. C 27.29%, O 72.71 % Occurs in the atms of many planets. In our solar system, e.g., on Venus, the optical layer thickness due to COj is 100,000 cm/atm, but only 220 cm/atm on Earth. Analyses of air in the temperate zones of the Earth show 0.027 to 0.036% (v/ v) of COj G. P. Kuiper, The Atmospheres of the Earth and the Planets (Univ. of Chicago Press, 1949) Landolt-Bornstein, Zahlenwerte vol. Ill (Springer-Verlag, 6th ed., 1952) pp 59 and 5g5. Constituent of carbonate type of minerals and products of animal metabolism. Necessary for the respiration cycle of plants and animals. Obtained industrially as a by-product in the manuf of lime during the "burning of... 

The alcohol has a piCa close to that of water, so hydroxide is not a good choice for complete deprotonation, and sodium hydride is commonly used for this purpose. Hydroxide will however deprotonate both the carboxylic acid, to make a carboxylate salt, or the ammonium ion, to make the free amine. Bicarbonate is also commonly used for this purpose although it is only just basic enough to do the job, the deprotonation reaches completion because it is not an equilibrium protonated bicarbonate forms carbonic acid which decomposes irreversibly to water and carbon dioxide. 

Carbon Acids. Active methylene compounds, such as mal-onates and 8-keto esters, can be deprotonated with sodium hydride and alkylated on carbon (eqs 12 and 13). Alkylation of Reissert anions is also facile with sodium hydride (eq 14). ... 

Carbon Acids. One of the more common uses of sodium hydride is the deprotonation of activated methylene compounds to generate highly reactive carbanions. A shuttle-deprotonation system has been described in which sodium hydride is the stoichiometric base and is used in conjunction with a crown ether cocatalyst to generate ketenes used in asymmetric catalysis. Enaminones can be converted to naphthyridinones using sodium hydride in THE (eq 47). ... 

The positively charged P atom stabilizes the negative charge on carbon, making phosphonium salts another class of carbon acids (to add to those you met In Chapter 8) that can be deprotonated by strong base. The hydride ion is the conjugate base of H2 which has a p/Tg of about 35. 

I. P. Beletskaya, L. S. German, and V. R. Polishchuk, J. Organometallic Ckem., 1970,25, 11. D. Holtz, Progr. Phys. Org. Chem., 1971, 8,1 (note that the acidities of fluorocarbon hydrides have been discussed recently by J. R. Jones in The Ionization of Carbon Acids , Academic Press, London and New York, 1973). 

The rates at which protons can be removed from transition metal hydrides (their "kinetic acidities") generally parallel their thermodynamic acidities pK values). However, the removal of a proton from a metal is much slower than the removal of a proton from an electronegative atom like nitrogen or oxygen. The reverse is also true the protonation of a metal (to form a hydride) is slower than the protonation of a nitrogen or an oxygen examples are shown in Equations 3.113 and 3.114. The low kinetic acidity of transition metal hydrides is much like that of carbon acids in organic chemistry. - - ... 

Information bearing on the interplay of factors liable to affect the stability of a fluorocarbahion continues to be sought, as revealed by two papers dealing with the determination of the kinetic acidities of a wide range of fluorocarbon hydrides or related carbon acids, (2S)—(28), by base-catalysed (EtjN) hydro n, doitmum, and tritium exchange methods (solvent system equimolar DMSO-MeOH or [ H,lDMSO-McOD mixtures). - The results further establish that the main factors to be considered are a-inductive... 

---