Carbon dioxide Lewis acid

Salts and esters of carboxylic acids are called carboxylates. When a carboxyl group is deprotonated, its conjugate base, a carboxylate anion is formed. Carboxylate ions are resonance stabilized and this increased stability makes carboxylic acids more acidic than alcohols. Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide under some circumstances they can be decarboxylated to yield carbon dioxide. 

Asymmetric addition of small-molecule nucleophiles to carbonyl groups and their derivatives are catalyzed by either Lewis acids or Lewis bases. Carbon dioxide is now a promising building block for as5mimetric organic synthesis. 

Soil Hydrolyzes in soil to 2-isopropyl-4-methyl-2-hydroxypyrimidine, diethylphos-phorothioic acid, carbon dioxide (Getzin, 1967 Lichtenstein et al., 1968 Sethunathan and Yoshida, 1969 Sethunathan and Pathak, 1972 Bartsch, 1974 Wolfe et al., 1976 Soma-sundaram and Coats, 1991) and tetraethylpyrophosphate (Paris and Lewis, 1973). The half-life of diazinon in soil was observed to be inversely proportional to temperature and soil moisture content (Getzin, 1968). Seven months after diazinon was applied on a sandy loam (2 kg/ha), only 1% of the total applied amount remained and 10% was detected in a peat loam (Suett, 1971). 

As a rule, no ions are produced when acids and bases are dissolved in relatively inert solvents such as benzene. The assumption of protective coatings to explain the absence of a reaction between metals and a solution of hydrogen chloride in benzene is unnecessary. In water, metals react more rapidly when an acid is present because of the increased concentration of solvent cations. The metal reacts slowly with water, even in the absence of the acid, but no such reaction takes place in benzene because there are no solvent cations mth which the metal can react. The statement is sometimes made that acids dissolved in inert solvents do not react with carbonates. But the reaction with carbonates is one that does not necessarily depend on solvent cations. It depends on the strength of the acid required to displace the weaker acid, carbon dioxide, from its compound. Lewis has shown that a strong acid like boron trichloride will displace carbon dioxide from sodium carbonate in a mixture of carbon tetrachloride and acetone. 

The hydrogen ions displace the weak acid, carbon dioxide, from combination with the oxide ion. Another example described by G. N. Lewis is the displacement of carbon dioxide when finely divided sodium carbonate is warmed with boron trichloride or stannic chloride in a mixture of carbon tetrachloride and acetone. The other product was not analyzed, but the reaction might be written tentatively as ... 

Many important biochemical reactions involve Lewis acid Lewis base chemistry Carbon dioxide is rapidly converted to hydrogen carbonate ion m the presence of the enzyme carbonic anhydrase... 

When a carbonyl group is bonded to a substituent group that can potentially depart as a Lewis base, addition of a nucleophile to the carbonyl carbon leads to elimination and the regeneration of a carbon-oxygen double bond. Esters undergo hydrolysis with alkali hydroxides to form alkali metal salts of carboxylic acids and alcohols. Amides undergo hydrolysis with mineral acids to form carboxylic acids and amine salts. Carbamates undergo alkaline hydrolysis to form amines, carbon dioxide, and alcohols. 

The production of steel begins when iron ore is fed into a blast furnace (Fig. 16.39). The furnace, which is approximately 40 m high, is continuously replenished from the top with a mixture of ore, coke, and limestone. Each kilogram of iron produced requires about 1.75 kg of ore, 0.75 kg of coke, and 0.25 kg of limestone. The limestone, which is primarily calcium carbonate, undergoes thermal decomposition to calcium oxide (lime) and carbon dioxide. The calcium oxide, which contains the Lewis base O2", helps to remove the acidic (nonmetal oxide) and amphoteric impurities from the ore ... 

The activity and stability of catalysts for methane-carbon dioxide reforming depend subtly upon the support and the active metal. Methane decomposes to carbon and hydrogen, forming carbon on the oxide support and the metal. Carbon on the metal is reactive and can be oxidized to CO by oxygen from dissociatively adsorbed COj. For noble metals this reaction is fast, leading to low coke accumulation on the metal particles The rate of carbon formation on the support is proportional to the concentration of Lewis acid sites. This carbon is non reactive and may cover the Pt particles causing catalyst deactivation. Hence, the combination of Pt with a support low in acid sites, such as ZrO, is well suited for long term stable operation. For non-noble metals such as Ni, the rate of CH4 dissociation exceeds the rate of oxidation drastically and carbon forms rapidly on the metal in the form of filaments. The rate of carbon filament formation is proportional to the particle size of Ni Below a critical Ni particle size (d<2 nm), formation of carbon slowed down dramatically Well dispersed Ni supported on ZrO is thus a viable alternative to the noble metal based materials. 

Flynn et al., also described the synthesis of the fused indoles [73]. The o-iodotrifluoroacetanilide 110 was coupled to aryl alkyne 111 under Sono-gashira conditions followed by subsequent reaction with aryl iodide, 107 with gaseous carbon dioxide produced the fused indole 158. Lewis acid dealkylation with aluminum trichloride produced the deprotected alcohol 159. 

Homogeneous Chemical Catalysis of the Reduction of Carbon Dioxide. Synergistic Effect of Bronsted and Lewis Acids... 

The direct electrochemical reduction of carbon dioxide requires very negative potentials, more negative than —2V vs. SCE. Redox catalysis, which implies the intermediacy of C02 (E° = —2.2 V vs. SCE), is accordingly rather inefficient.3 With aromatic anion radicals, catalysis is hampered in most cases by a two-electron carboxylation of the aromatic ring. Spectacular chemical catalysis is obtained with electrochemically generated iron(0) porphyrins, but the help of a synergistic effect of Bronsted and Lewis acids is required.4... 

Chemical/Physical. Emits toxic phosgene fumes when heated to decomposition (Sax and Lewis, 1987). In a 0.50 N sodium hydroxide solution at 20 °C, chlorpropham hydrolyzed to aniline derivatives. The half-life of this reaction was 3.5 d (El-Dib and Aly, 1976). Simple hydrolysis leads to the formation of 3-chlorophenylcarbamic acid and 2-propanol. The acid is very unstable and is spontaneously converted to 3-chloroaniline and carbon dioxide (Still and Herrett, 1976). 

Ligands that can coordinate to an active center in an enzyme and prevent coordination by the substrate will tend to inhibit the action of that enzyme. 1 We have seen that azide can occupy the pocket tailored to fit the carbon dioxide molecule. This prevents the latter from approaching the active site. Furthermore, the infrared evidence indicates that the azide ion actually does bind the zinc atom The asymmetric stretching mode of the azide ion is strongly shifted with respect to the free ion absorption. Thus the zinc is inhibited from acting as a Lewis acid towards water with the formation of a coordinated hydroxide ion. Other inhibitors also bind to the metal atom. As little as 4 x I0-6 M cyanide or hydrogen sulfide inhibits the enzymatic activity by 85%. 

Hydroxide ion Carbon dioxide (Lewis base) (Lewis acid)... 

The carbon dioxide molecule exhibits several functionalities through which it may interact with transition metal complexes and/or substrates. The dominant characteristic of C02 is the Lewis acidity of the central carbon atom, and the principle mode of reaction of C02 in its main group chemistry is as an electrophile at the carbon center. Consequently, metal complex formation may be anticipated with basic, electron-rich, low-valent metal centers. An analogous interaction is found in the reaction of the Lewis acid BF3 with the low-valent metal complex IrCl(CO)(PPh3)2 (114). These species form a 1 1 adduct in solution evidence for an Ir-BF3 donor-acceptor bond includes a change in the carbonyl stretching frequency from 1968 to 2067 cm-1. 

Many oxides of nonmetals are gaseous molecular compounds, such as C02, NO, and S03. Most can act as Lewis acids, because the electronegative oxygen atoms withdraw electrons from the central atom, enabling it to act as an electron-pair acceptor. For instance, carbon dioxide can react with the oxides of metals because the oxide ion in the metallic oxide is a strong Lewis base ... 

Prior to a discussion of C02 insertion reactions into M-H and M-C bonds it is useful to review some of the known coordination chemistry of carbon dioxide, since activation of COz by metal centers is assumed to be of significance in most of these processes. Carbon dioxide can interact with metal centers by three functionalities. These include the Lewis acid site at carbon (1), the Lewis base sites of the terminal oxygen atoms (2), and the t]2 C=0 bond (3). It is possible as well that a combination... 

In coordinatively saturated metal hydrides, such as the HM(CO)s (M => Cr, Mo, W) derivatives, formation of the four-centered transition state for C02 insertion (Scheme 1) may proceed with or without CO loss and concomitant coordination ofC02 at the metal center. That is, C02 insertion may occur by means of dissociative (D) or dissociative interchange (Id) processes, or an associative interchange (Ia) process (47, 48). In either instance an acid-base interaction between the anionic hydride ligand and the electrophilic carbon center of carbon dioxide as represented in 6 may occur prior to formation of the four-centered transition state depicted in Scheme 1. An interaction of this type has been observed for these HM(CO)j derivatives with Lewis acids such as BH3 (49). 

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