[GinaTageldin]

hello guys ,
i had a problem upon oxidation of an aromatic heterocyclic aldehyde (substituted pyrazole aldehyde )by KMNO4 and in presence of 50% pyridine at room temp it gives an product this method was reported in case of this acid
when i enter this acid in estrification by SOCl2 and ppt it becomes waxy substance but pure
so, i suggested that to use only KMNO4 while heating at 80 and it gives an product differ in spotting on tlc and m.p from acid obtained from pyridine procedure , what was happened it on of them is an intermediate to the other specially in both tlc during reaction had small faint spot of the other but upon separation on only the major separated and the faint disappear
what is happening and which one of them is the acid and what is the intermediate
in adddtion i have  thiophen ring as a substituent what is the role of pyridine ??

[orgopete]

Give us some help by posting the reaction schemes.

[GinaTageldin]

this is structure hoping to convert aldehyde gp to carboxylic acid

[GinaTageldin]

it is reported that converted to acid through KMNO4 and 50% pyidine at room temp but m.p was not clear in the paper while trying the other method KMNO4 excess and heating at 80 , different spotting why any other susceptible gp for oxidation , please help

[GinaTageldin]

this is the paper but i think the reported acid m.p is wrong or written mistake

[pgk]

Excess of KMnO4 in acid may further oxidize  thiophene to S,S-dioxide and even pyrazole to N–oxides. Pyridine is a base that stops KMnO4 reduction to MnO2 instead of Mn2+ and thus, KMNO4 in aqueous pyridine is a milder oxidizing agent.
Nitrogen containing polar molecules often form waxy solids, when dissolved in n-hexane. Try another recrystallization solvent system.

[GinaTageldin]

thank u Sir  , i get it know but l had a further question did the N give oxide even it has complete valency and did SO2 of the thienyl ring stable for futher estrification and acid hydrazide formation
also the ester was pure so enters into rection directly with no crystallization but its problem is when acid and alchol and SOCL2 added is turns greeny waxy during reflux and after sepration did u think is it the effect of residual pyridine from the step b4 but SOCl2 is acidic and neutralize any xss pyridine also ester  m.p= 80 or less
and another question in all cases KMNO4 converted to Mno2 upon any reaction in presence or absence of pyridine specially i tried this method xss and heating in another derivative (CH3 instead of theinyl ring )it was reported and works?

[pgk]

1a). Under acidic aqueous conditions:
KMnO4 → MnO2 → Mn2+
1b). Under basic aqueous conditions:
KMnO4 → MnO2 → Mn(OH)2 → Mn
Please, take a look to the above half equations and the corresponding voltages, from tables of various sources and then, you will clearly understand the role of pyridine.
2). During oxidation reaction, the oxidant is added in accordance of the oxidation number equilibrium and not at a molar ratio.
3). Thiophene oxidation steps:
Thiophene S-oxide→Thiophene S,S-dioxide→Semisuccinic-suflonic acid (HO3SCH2CH2CO2H)
4). During oxidation reaction, nitrogen containing moieties might be oxidized to the corresponding N-oxides by the excess of the oxidizing agent. However, low amounts of N-oxides side products, can be reduced by shaking with fresh iron powder or fresh zinc powder (Attention: this might be dangerous with flammable solvents (low flash point) and in absence of water}.
5). According the “good laboratory practice” and in a multi-step synthesis, a compound must be highly purified before being introduced in the next step (that makes life, easy). Especially in cases of biological and pharmaceutical interest, where the purity of the product is more important than the yield.