3.5- Dinitrobenzoyl chloride reagent

NOTE. The dinitrobenzoyl chloride reagent tends to hydrolyze on storage to form the corresponding carboxylic acid. Check its melting point before use (3,5-dinitrobenzoyl chloride, mp = 74 °C 3,5-dinitrobenzoic acid, mp = 202 °C)... 

The melting points of these esters are usually much lower than those of the corresponding 3 5 dinitrobenzoates their preparation, therefore, offers no advantages over the latter except for alcohols of high molecular weight and for polyhydroxy compounds. The reagent is, however, cheaper than 3 5 dinitrobenzoyl chloride it hydrolyses in the air so that it should either be stored under light petroleum or be prepared from the acid, when required, by the thionyl chloride or phosphorus pentachloride method. 

Excess of the reagent should be avoided, if possible. If excess of dinitrobenzoyl chloride is used, this appears as the acid in the precipitate obtained upon acidih-... 

Derivatives of higher melting point may be obtained withp-nitrobenzoyl chloride the experimental details are similar to those given above for benzoyl chloride. 3 5-Dinitrobenzoyl chloride (Section 111,27,7) may also be used glycerol gives unsatisfactory results with this reagent. 

Mix 0-2 g. of 3 5-dinitrobenzoyl chloride, 6 drops of the mercaptan and 1-3 drops of pyridine in a test-tube, and heat the mixture in a beaker of boiling water until fumes of hydrogen chloride cease to appear (15-30 minutes). Add a few drops of water, followed by a drop or two of pyridine to eliminate the excess of the reagent. The product sohdifies upon stirring with a glass rod. Add water, filter, and recrystalUse from dilute alcohol or dilute acetic acid. 

Apply 10% 3,5-dinitrobenzoyl chloride solution [72] in p-xylene — tetrahydrofuran (15-1-2), followed by sample solution allow to react destroy excess reagent with 10% sodium hydroxide solution. 

Suitable reagents for derivatizing specific functional groups are summarized in Table 8.21. Many of the reactions and reagents are the familiar ones used in qualitative analysis for the characterization of organic compounds by physical means. Alcohols are converted to esters by reaction with an acid chloride in the presence of a base catalyst (e.g., pyridine, tertiary amine, etc). If the alcohol is to be recovered after the separation, then a derivative which is fairly easy to hydrolyze, such as p-nltrophenylcarbonate, is convenient. If the sample contains labile groups, phenylurethane derivatives can be prepared under very mild reaction conditions. Alcohols in aqueous solution can be derivatized with 3,5-dinitrobenzoyl chloride. 

General methods for the preparation of acid halides from aliphatic carboxylic acids are described in Section 5.12.1, p. 692. Phosphorus pentachloride is the preferred chlorinating agent for aromatic acids which contain electron-withdrawing substituents, and which do not react readily with thionyl chloride. The preparation of both p-nitrobenzoyl chloride and 3,5-dinitrobenzoyl chloride is described in Expt 6.161. These particular acid chlorides are valuable reagents for the characterisation of aliphatic alcohols and simple phenols, with which they form crystalline esters (see Section 9.6.4, p. 1241 and Section 9.6.6, p. 1248). 

Selective reduction of functional groups can be achieved by chemical modification of the LiALH4 for example, lithium tri(t-butoxy)aluminium hydride [LiAIH(t-OBu)3] is a more selective reagent, and reduces aldehydes and ketones, but slowly reduces esters and epoxides. Nitriles and nitro groups are not reduced by this reagent. Carboxylic acids can be converted into the aldehyde via acid chloride with lithium tri(tert-butoxy) aluminium hydride at a low temperature (—78°C). The nitro compounds are not reduced under this condition. Thus, selective reduction of 3,5-dinitrobenzoic acid (6.45) to 3,5-dinitrobenzaldehyde (6.47) can be achieved in two steps. First, 6.45 is converted into 3,5-dinitrobenzoyl chloride (6.46) and then LiAlH(t-OBu)3 reduction of 6.46 gives 6.47. 

Various derivatization reagents have been developed and used as labeling reagents for traces of primary and secondary aliphatic amines in HPLC, including OPA, 3,5-dinitrobenzoyl chloride,... 

Reagents i, NaBH4 ii, AcjO-pyridine iii, Collins reagent iv, Na-n-CsHuOH v, 0s04-pyridine-diethyl ether vi, 3,5-dinitrobenzoyl chloride-pyridine vii, OH ... 

U,5-Dinitrobenzoyl chloride is an acid chloride and hydrolyzes readily. The purity of this reagent should be checked before its use by determining its melting point (mp 69-71 C). When the carboxylic acid is present, the melting point will be high. 

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