[OhMyGod]

Hi dudes. just a few qns. Pls be patient with me LOL! 

The first question.

How do u get Propanoic Acid from Ethanal. My idea is to first let the Ethanal undergo nucleophilic addition with NaCN to form CH3CHOHCN. Then let it undergo Acidic Hydrolysis to form CH3CHOHCOOH . Next, let it the alcoholic -OH part undergo dehydration to form the CH2=CHCOOH. and Finally, let it undergo reduction with H2 + nickel catalyst, forming our propanoic acid. CH3CH2COOH.

My 2nd question is different from the first. As you guys know MethylBenzene becomes benzoic acid after undergoing reflux with acidificed KMnO4. and this applies to any Benzene ring connected to a R Group. Just wondering whether if this still applies to C6H5-0-CH2OH, with the O atom in the middle.

Thanks in advance for the help people.!

[kiwi]

in your synthesis, (if the gods were smiling) you could hydrolyse the cyano group and eliminate the hydroxyl group in the one operation (heat with conc acid), so really your route is only three steps. i can think of a few 4 step sequences, but none shorter than 3.

[OhMyGod]

Lol from what i learnt. you can really hydrolyse the Cyano group and turn it into -COOH functional group, its under acidic hydrolysis. and The Hydroxyl group can indeed be eliminated(170C + conc h2SO4).

well tell me whats wrong  and maybe type out the synthesis thats on your mind, so that i can learn. ^^
otherwise, i would have really no clue...

thx for the reply.

(note: just thought of it. the new sythesis ive tot of is by Nucleophilic addition using NaCN. secondly, adding PCl5 to replace -OH with -Cl. then carry out DEhydrohalogenation to get the alkene double bond. Then, reduction using H2+nickel. lastly, acidic hydrolysis to replace -CN with -COOH.)

How abt this? and i still cant see why the first method i suggested is wrong :O

[kiwi]

no the first method isn't wrong - i was pointing out that it is pretty efficient being only three steps. your method would work.
i've thought of a two step synthesis, but it uses less straightforward chemistry so i still think your answer is better (ethanal to propanal via the enolate/MeI, then oxidation propanal->propanoic acid)

[OhMyGod]

Oh i see dude....

Regarding the hydrolysation of -CN to -COOH and at the same time the elimination of -OH in one step(heat with conc h2s04 at 170), Is it possible? since the conditions for -CN to -COOH is only heating with dil. H2S04.

and regarding the 2nd question ive asked in the first post
 

My 2nd question is different from the first. As you guys know MethylBenzene becomes benzoic acid after undergoing reflux with acidificed KMnO4. and this applies to any Benzene ring connected to a R Group. Just wondering whether if this still applies to C6H5-0-CH2OH, with the O atom in the middle.

Do you happen to have a solution?

Thanks mate for the kind *delete me*

[Fry]

Reduction of aldehyde to produce primary alcohol.
Substitution with SOCl2 to produce the primary halide.
Create a grignard reagent and attack solid CO2.

Sounds reasonable to me, what do you think?

[Dan]

(ethanal to propanal via the enolate/MeI, then oxidation propanal->propanoic acid)

Yeah, this was my initial thought too. Lots of good suggestions.

I'd like to point out that if you want to form a cyanohydrin from an aldehyde with NaCN, and eliminate in acidic conditions in the same pot, you'd have to be immensely careful. Rule no. 1 for working with cyanide is that you do not, unless absolutely necessary put and acid in your reaction vessel. HCN is not good for you!

[OhMyGod]

thanks for the help dan and fry. just a little concern abt the sythesis ive suggested which is this

My idea is to first let the Ethanal undergo nucleophilic addition with HCN to form CH3CHOHCN. Then let it undergo Acidic Hydrolysis to form CH3CHOHCOOH . Next, let it the alcoholic -OH part undergo dehydration to form the CH2=CHCOOH. and Finally, let it undergo reduction with H2 + nickel catalyst, forming our propanoic acid. CH3CH2COOH.

just wondering whether the last step which is the hydrogenation with CH2=CHCOOH (with reagents H2 + Nickel Catalyst) will in turn reduces the -COOH to aldehyde as H2+Nickel is a reducing agent.