Acids 45 Group

Typical organic acids contain the --C(0)0H group, but many other acid groupings, e.g. the sulphonic -S(0)20H give acidic properties to organic compounds. Phenols have acidic properties and are classified with enols as pseudo-acids. 

This ordering is the same as discussed above for anionic surfactants and follows from the charge density of the particular acid group. 

As an example, the empirical formula of phenylalanine may be split into a more extended form that shows the presence of a phenyl ring, as well as an amino and a carboxylic acid group (the condensed form in Figure 2-4). 

When the phenol contains a carboxylic acid group, e.g., m- or p-hydroxy-benzoic acid, the acetylated derivative will of course remain in solution as the sodium salt, but is precipitated when the solution is subsequently acidified. Salicylic acid, however, cannot be acetylated under these conditions. 

Sodium carbonate solution [cf. Section 5, p. 330). Note that phenols (except those containing acidic groups, e.., nitrophenols) give no reaction with sodium carbonate solution. 

Method. An amino-acid such as glycine, NHjCH,COOH, cannot be estimated by direct titration with standard alkali solution, owing to the opposing effects of the basic and the acidic groups. If, however, the amino-acid is first... 

The azo dyes are not of any great practical value owing to their slight solubility in water. Th4 introduction of a sulphonic acid group into the molecide has no effect upon the colour, but renders the dye water-soluble—a fact of great commercial value. The simplest way of achieving this is to employ an amine, e.g., sulphanilic acid, in which the — OjH group is already present. 

Picric acid, the 2 4 6-trinitro derivative of phenol, cannot be prepared in good yield by the action of nitric acid upon phenol since much of the latter is destroyed by oxidation and resinous products are also formed. It is more convenient to heat the phenol with concentrated sulphuric acid whereby a mixture of o- and p-phenolsulphonic acids is obtained upon treatment of the mixture with concentrated nitric acid, nitration occurs at the two positicsis mela to the —SOjH group in each compound, and finally, since sulphonation is reversible, the acid groups are replaced by a third iiitro group yielding picric acid in both cases ... 

RCH(OH)=CHCOR or -keto esters RCH(OH)=CHCOOR ) dissolve in dilute sodium hydroxide solution, i.e., contain an acidic group of sufficient strength to react with the alkah. Carboxyhc acids and sulphonic acids are soluble in dilute solutions of sodium bicarbonate some negatively-substituted phenols, for example, picric acid, 2 4 6-tribromo-phenol and 2 4-dinitrophenol, are strongly acidic and also dissolve in dilute sodium bicarbonate solution. 

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

Similar halogenations have been done on 2-lithio-l-phenylsulfonylindole[2], 2-Lithio-l-phenylsulfonylindole is readily converted to the 2-(trimethylsilyl) derivative[2,3]. 2-Trialkylstannylindoles can also be prepared via 2-lithio-indoles[4,5], 2-Sulfonamido groups can be introduced by reaction of a 2-lithioindole with sulfur dioxide, followed by conversion of the sulfinic acid group to the sulfonyl chloride with A-chlorosuccinimide[6]. 

Sulfonation Treatment of benzene with hot concentrated sulfuric acid gives benzenesulfonic acid A sulfonic acid group (—SO2OH) replaces one of the ring hydrogens... 

Sulfonic acid groups are electron withdrawing because sulfur has a formal posi tive charge in several of the resonance forms of benzenesulfomc acid... 

When benzene undergoes disulfonation m benzenedisulfomc acid is formed The first sulfonic acid group to go on directs the second one meta to itself... 

The reaction of aldoses with nitric acid leads to the formation of aldaric acids by oxidation of both the aldehyde and the terminal primary alcohol function to carboxylic acid groups Aldaric acids are also known as saccharic acids and are named by substi tutmg aric acid for the ose ending of the corresponding carbohydrate... 

Uronic acids occupy an oxidation state between aldonic and aldanc acids They have an aldehyde function at one end of their carbon chain and a carboxyhc acid group at the other... 

The most acidic proton is the one of the carboxylic acid group and should have a of approx imately 5... 

Examine the unfilled valences of the carboxylic acid group and find the one marked by a small circle If necessary click on the group to make this circle move to the va lence on carbon... 

The carboxylic acid group has two struc turally distinct valences that can be used to connect this group to the model The active valence is marked by a small cir cle and can be changed by clicking any where on the group... 

A new carbon-carbon bond forms and an entire carboxylic acid group is added to the model... 

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

A suitable functional group is assayed in the same sample. In general chemistry and many polymer applications, this is merely the titration of acid groups with a base, or vice versa. Note that only volumetric glassware and a method for end point determination are required to do this. 

From the volume and concentration of the base, the number of equivalents of the neutralized acid group is readily calculated. 

Only acid groups are titrated and two ends are counted per molecule. 

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