DIAZOTISATION TITRATION OR NITRITE TITRATIONJ.S.K. NAGARAJAN,email: firstname.lastname@example.orgPh: 09443149945
DIAZOTISATION TITRATION Difference between AZO &AZO: AZAAZA:Nitrogen present & Nitrogen present &linked in open chain linked in inside chain. -N=N-Aromatic & Aliphatic Eg: Nitrogen containingamines Heterocyclic compounds Eg: Amaranth Eg: Pyridiazine, Pyrazole.
DIAZOTISATION TITRATIONQualitative Analysis of amines with HNO 2 :Amine +conc. HCl & cool to 0 - 5 in ice-bath for 5 minutes. Addcold solution of NaNO2 keep in ice-bath.Pri. Ali amine : N 2 evolved. Diazoniium will not form.RNH2 + HNO2 -> ROH + N 2 + H2OBut, with -15 C Diazonium salt forms.Pri. Ar. Amine: Diazonium salt forms.ArNH2 +HNO2 ------- ArN=N+ClCold diazonium solution & + cold solution of 2-naphthol inNaOH solution. An orange-red azo dye is formed.PRINCIPLE: DIAZO & COUPLINGSec. Ali. & Sec. Ar. Amine---Yellow oily Nitrosaminesforms. R 2 NH + HNO 2 -----> R 2 N-NOTert. Ali.:-- No reaction.Tert. Ar.: Green p-nitroso compounds (if p-position unsubstituted).
DIAZO TITRATIONS:REQUIREMENT: For Diazo Titration - Ar. PrimaryAminePROCEDURE:Ar pri amines +NaNO2 in acidic solutions to formdiazonium salts. HClC6H5NH2 + NaNO2 C6H5N2Cl+ NaCl + 2H2OEnd point detected by presence of small amounts ofnitrous acid- By using starch iodide as indicator.
Diazotization Titrations - PRINCIPLE HCl C6H5NH2 + NaNO2 C6H5N2Cl+ NaCl + 2H2O NaNO 2 + HCl HNO 2 + NaCl Nitrous acid form interaction of sodium nitrite with HCl KI + HCl HI + KCl 2HI +2HNO 2 I 2 +2NO +2H 2 (small excess of HNO 2 )Liberation of iodine from iodide Small excess of HNO2 present at End point detection by two methods: – Visual end point (Starch Iodide paper/paste) – Amperometrically (dead-stop end-point technique)5
Diazo Titration - ElectrometricPrinciple:Immerse Platinum electrodes in titration liquid.Electrode polarization occurs in titration liquid.Electrode polarization occurs when a small voltage (30-50mμ) is applied across electrodes & no current flows thruthe sensitive galvanometer included in circuit, during thecourse of titration.Liberation of excess of HNO2 at the end point depolarizeselectrode, current flows & full deflection in galvanometerneedle is observed. Known as dead stop end point .Method :Sample + dissolve in HCl & water. Insert platinumelectrodes into solution, connected thru sensitivegalvanometer & suitable potentiometer at 2V battery insuch a way as to produce potential drop between 30-50mμ across the electrodes.Titrate slowly with N/10 NaNO2 with continuous stirring untila permanent deflection of the galvanometer is observed atthe end point.
Diazotization Titrations - PRINCIPLE HCl C6H5NH2 + NaNO2 C6H5N2Cl+ NaCl + 2H2O NaNO 2 + HCl HNO 2 + NaCl Nitrous acid form interaction of sodium nitrite with HCl KI + HCl HI + KCl 2HI +2HNO 2 I 2 +2NO +2H 2 (small excess of HNO 2 )Liberation of iodine from iodide I 2 + STARCH Blue color Starch Iodide paper/paste used as external indicator. Because if we add starch iodide paste in conical flask as internal indicator, it react & gives blue color in the beginning of the titrations itself. This lead to the confusion. Instead, starch paste is applied in paper/starch iodide paper- used to detect end point. Reaction mixture is withdrawn from the conical flask after the addition of HNO2 to the conical flask. And after every few ml HNO2 added from the burette to the conical flask, then the mixture withdrawn & dropped on the starch paste/starch iodide paper, when there is sudden change in color,7 the addition HNO2 is stopped..
Standardisation of Sodium NitriteTheory :HNO2 obtained from addition of NaNO2 into acidicreaction mixture, reacts with Pri. NH2 group ofsulphanilamide , form diazonium salt (unstable).Reaction not maintained between 5-10°C - undergodecompositionAt the equivalence point slight excess of HNO2 is presentNaNO2 + HCl → HNO2 + NaClwhich must persist for at least 1 minute. Excess HNO2detected by starch iodide paper/paste. 2I– + 2HNO2 + 2H+ → I2 + 2NO + 2H2OProcedure : Suphanilamide in beaker +20 ml HCl +water. Dissolved & cool to 5°C in ice-bath. Titrate with Std. NaNO2, stirring vigorously Titrate continuously until produces blue starch-iodide paper Each 0.01722 g of sulphanilamide is =1ml of 0.1 N NaNO2.
Diazo Titration- AssayWeigh the sample & dissolve in mixture ofwater & HCl + KBr. Cool in ice.Immerse platinum electrodes in the solution& apply voltage about 50mV across electrodeswhen polarisation of electrodes takes place.Place burette tip just above the surface ofsolution & stir, maintaining temp. at 0-5ºTitrate with Std. NaNO2 slowly & when thetitration is within 1 ml of the end point, addtitrant in 0.1 ml portions, allowing NLT 1minute between additions.(galvanometer needle deflects & returns to approximatelyits original position until end point is reached).At the end-point, when a slight excess ofNaNO2 is present, the electrodes aredepolarised, current flows and a permanentdeflection of the needle is obtained.