Compounds with More Than One Acidic Group

5 Compounds with More Than One Acidic Group 

The benzenedisulfonic acids are of little interest, except that benzene-1,3-disulfonic acid is a source of 1,3-dihydroxybenzene (see Chapter 4). The benzene dicarboxylic acids are more important. Benzene-1,2-dicarboxylic acid (phthalic acid, 8) can be converted into phthalic anhydride (9), which is a typical acid anhydride, reacting with amines and alcohols and also taking part in Friedel-Crafts reactions. Phthalimide (10), produced by reaction of the anhydride with ammonia, is weakly acidic and forms a potassium salt with ethanolic potassium hydroxide. 

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The condensation reaction between carboxylic acid and alcohol to form an ester and water is a fundamental chemical reaction, and has been known at least from when the term organic chemistry was coined in the early nineteenth century. From the mid- to late-nineteenth century, studies were carried out on the reactions of compounds containing more than one acid group with compounds containing more than one hydroxyl group. These studies produced the first polyester resins, and lead to the development in the early twentieth century of various thermoset polymers such as the alkyd resins. 

With Lewis acids as catalysts, compounds containing more than one alkoxy group on a carbon atom add across vinyl ether double bonds. Acetals give 3-alkoxyacetals since the products are also acetals, they can react further with excess vinyl ether to give oligomers (228—230). Orthoformic esters give diacetals of malonaldehyde (231). With Lewis acids and mercuric salts as catalysts, vinyl ethers add in similar fashion to give acetals of 3-butenal (232,233). 

Fischer projections are especially useful in the case of compounds with more than one chirality center. For example, it is easy to see the plane of symmetry in meso-tartaric acid. As was the case with regular structures, interchanging any two groups in a Fischer projection results in inversion of configuration at the chirality center. Thus, interchanging the H and OH on the lower chirality center of weso-tartaric acid inverts the configuration at that chirality center, resulting in the (27 ,3R)-stereoisomer, (-i-)-tartaric acid. It is also easy to see that this stereoisomer does not have a plane of symmetry. 

At present nitration is one of the most widely applied direct substitution reactions. This is due to several factors. For example nitration usually proceeds easily, its products can readily be separated from the spent acid, said there is a wide range of possibilities in the practical use of nitro compounds, both as intermediates and end products. The presence of a nitro group in the starting product made it possible to obtain a number of basic organic intermediates such as aniline said benzidine. Dyes with more than one nitro group, such as picric acid were obtained. It has been found that higher nitrated nitro compounds and nitric acid esters have explosive properties and are of practical importance. Some nitro compounds are used in perfumes. Medicinal properties have lately been discovered in certain nitro compounds, eg. chloramphenicol. 

Substrates with more than one alkyl group are oxidized to dicarboxylic acids. Compounds without a benzylic C-H bond are inert to oxidation. 

Reactions of compounds containing more than one R group proceed stepwise, allowing intermediate products to be obtained if a deficiency of HX is used [e.g., Eq. (i)]. Rates of bond scission vary also, usually the ease of cleavage is M—aryl>M—alkyl. Cleavage of nonmetal element-C bonds with protonic acids can occur ... 

Acetoiicetyliition Reactions. The best known and commercially most important reaction of diketene is the aceto acetylation of nucleophiles to give derivatives of acetoacetic acid (Fig. 2) (1,5,6). A wide variety of substances with acidic hydrogens can be acetoacetylated. This includes alcohols, amines, phenols, thiols, carboxyHc acids, amides, ureas, thioureas, urethanes, and sulfonamides. Where more than one functional group is present, ring closure often follows aceto acetylation, giving access to a variety of heterocycHc compounds. These reactions often require catalysts in the form of tertiary amines, acids, and mercury salts. Acetoacetate esters and acetoacetamides are the most important industrial intermediates prepared from diketene. 

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