Functional Group Analysis

Functional Group Analysis

• Classical methods of analysis (wet chemical analysis)

analyte + reagent = color or ppt. Main steps: 1. sampling 2. field sample pretreatment 3. Laboratory tretment 4. Laboratory assay 5. Calculation 6. Result presentation

Instrumental methods Involve the use of instrument They are: 1. Spectral 2. Electro-analytical3. Separatory

Classical qualitative analysis

Classical quantitative analysis

Classical qualitative analysis

To deduce the identity of the analyte Add reagents that chosen one or single class of chemical compounds

(selectivity ) Form ppt. or a gas or color with reagent Other measurements as b.p, m.p, , density …. Examples: addition of Br2 to identify the C=C…. Reaction used to identify the organic molecules

(condensation, diazodization, diazocoupling….)

Classical quantitative analysis

Volumetric analysis (titrimetric analysis) : acid – base , redox , complexometric, preciptmetry that give change in colour with indicator at the e.p at certain volume of titrant Gravimetric analysis: form ppt. with analyte , filtred, dried and weighed

Examples of functional group analysis

- OH - C=O - COOH 1. Acylation

(esterification)2. Non-aqueous titration3. Bromination4. Periodic acid oxidation5. spectrophotometry

1. Oximation 2. Hydrazone formation 3. Condensation with

active methylene

1. Acid – base titration2. Saponification 3. Reaction with ferric

hydroxamete

Amines Thiol Others 1. Acid – base titration2. Condensation (1ry amine) with

carbonyl compounds 3. Reaction with 9-chloroacridine 4. With formaldehyde/acetone 5. Diazotization and diazocoupling 6. Charge – transfer 7. Ion-pair complexation

1. AgNO3

2. Br2

1. Zeissel method for OR/N-alkyl group

2. Drug with reducing activity

3. Binary complex formation

4. Ternary complexation reaction

Hydroxyl group –OH alcoholic, glycols, enols and phenols

1. Acylation (esterification):

Acid chloride or acid anhydride is used as they more potant than the parent acid

acid alcohol ester

2. Non aqueous titration Phenols and enols are weak acidic compounds can dermined by titration with NaOCH3 in DMF and thymol blue as indicator

3. Bromination of phenolic compounds

The excess bromine liberate iodine from KI and titrated against NaS2O3 using starch as indicator

Aromatic amines undergo the same reaction so interfere in this analysis. Also unsaturated compounds interfere by addition of bromine

4. Periodic acid oxidation of 1,2- glycol

Propylene glycol: CH3CHOHCH2OH + 2 HIO4 = CH3CHO + HCHO + HIO3 + H2O

excess KI I 2 titrated using Na2SO4

Glycerol NaOH CH2OH-CHOH-CH2OH + 2HIO4 = 2CH2O + HCOOH + 2HIO3 + H2O

HCOOH + NaOH = HCHO + H2O

1 glycerol = 1 NaOH using bromocresol green as ind. (dis. Glycol)

5. Spectrophotometry

1. By coupling with Diazonium salt (azo dye)2. Nitrosation 3. Coupling with antipyrine in presence of oxidizing agent

Carbonyl group –C=Oaldehyde/ ketons

1. Oximation Oximes can be formed by the action of hydroxylamine on aldehydes or ketones

2. Hydrazone formation

3. Condensation with Active methylene group

• Aldehyde and ketones form highly conjugated reaction product with these reagents

Knoevenagel condensation

Chlorobenzaldehyde Yellow colour product

Carboxylic acid and their derivative- COOH

RCOOH RCOOR’RCONHR’RCONHCOR’ (imide)(RCO)2ORCOCl

Carboxylic acid

Ester

Amides

imide

Carboxylic-acid-anhydride

Acyl-chloride

1. Acid – base titration2. Saponification 3. Ferric hydroxamate (Esterification and the hydroxamic acid test)

Esters react with hydroxylamine in basic solution to form hydroxamic acids, which in turn react with ferric chloride in acidic solution to form bluish red ferric hydroxamate

Amines – NH

1ry amine 2nd amine 3rd amine1. Condensation with carbonyl

compounds 2. Reaction with 9-chloroacridine 3. formaldehyde/acetone 4. Diazotization and diazocoupling

CS2 + KOH + Cu 1. Charge – transfer 2. Ion-pair complexation

1. Primary amine:

1. Condensation with carbonyl compoundSchiff’s base (spectrophotometry)

2. Reaction with 9- chloroacridine:

3. Reaction with formaldehyde/ acetone

• Hantzsch pyridine synthesis

Reaction with dansyl chloride (dansylation)

Fluorescent product

4. Diazotization and diazo-coupling

2. Secondary amine:

3. Tertiary amines • Charge transfer method: Complexes between , Electron donor (amines and their derivatives): electron acceptor (chloranil, p-chloranailic acid, iodine ….)

Acceptor Donner

• Ion – pair complex

AB B+ + A-

Amines methyl orange, bromothymol blue ,

salicylate …. famotidine

Thiol, sulphide, disulphide -SH , RSR, RSSR

RSH + AgNO3 = RSAg + HNO3

RSR + Br2 = RSOR + HBr

RS-SR + Br2 = 2 RSO2Br +HBr

Miscellaneous

1. Zeisel’s method (for Alkoxy OR, and N-Alkyl):alkoxy group is treated with hydrogen iodide and the alkyl halide formed is further treated with silver nitrate to precipitate silver iodide, collected and weighed

CH3OC2H5 + 2 HI = CH3I + C2H5OH Volatile

Methyl or ethyl iodide only

indomethacin

piroxicam

2. Drugs with reducing activity:

When 1,10-phenanthroline is added to even a dilute solution of iron(II), the highly colored complex ion [Fe(phen)3]2+ is produced.

3. Binary complex:Drugs containing NH2 and - COOH form complex with Metals extractable with organic solvent . Example mefenamic and flufenamic acid contain NH and COOH form blue colour complex with copper in alkaline medium and purple with iron in acid medium

4. Ternary complex formation (Ln Mx Sy) Used in spectrophotometric analysis More sensitive than the birany complex The complex of SCN, Cr(III), Zn(II), Co(II), Fe(III) are widely used.

metal

OfloxacineDrug

Ligand

(Ln Mx Sy)