[matt1234]

Hello,
Can someone please look this reaction over and let me know if i have done it correctly?  I have a test tommorrow and this question is likely to be there.

Thank for your time.
Matt

[cliverlong]

I find organic synthesis questions hard.

The only reference I can find to benzanal synthesis is

http://en.wikipedia.org/wiki/Gattermann-Koch_reaction

which is a "type" of Friedel Crafts alkoylation of benzene where the unstable methanoyl chloride is formed in situ.

I don't know from which ester you would start to end up with a methnal side chain

my guess would be (working from the information here: http://en.wikipedia.org/wiki/Benzoic_acid#Carboxyl_group)

ester of benzoic acid and ethanol > Acid hydrolysis to release benzoic acid > PCl₅ to change carboxylic acid to acyl chloride > someway to remove Cl without replacing with an OH group and regenerating the benzoic acid 

[sjb]

Especially at the high school level, this is going to be difficult to predict, as although there are probably many ways to make aldehydes, you probably haven't come across many of them so they may be confusing. Which books are you using? What ways of making aldehydes in general do you know?

I'm virtually certain that the way you've proposed will not work, but to explain may involve concepts you have not covered yet.

[matt1234]

Hello,

Thanks for the help, Here is an E Book of my text: http://www2.kpr.edu.on.ca/cdciw/science/12U_chemistry/12U%20chemistry%20textbook/default.html

Organic chemistry is the very first chapter, this is the first time i have been exposed to organic chemistry, so im sure the concepts are still very basic.

Thanks again.
Matt

Not that question is from the last section in chapter 1 pg 82

[Dan]

Ok, I had a quick look at your book and it seems as though for methods of making aldehydes, you have covered "controlled oxidation" of primary alcohols right?

1. Which primary alcohol would undergo controlled oxidation to benzaldehyde?
2. How could you get an alcohol from an ester?

[matt1234]

1. Which primary alcohol would undergo controlled oxidation to benzaldehyde?


A:  i would use phenylmethanol

2. How could you get an alcohol from an ester?

For this one i would say do the same thing i wrote on my answer sheet above^ .  I thought making a salt and alcohol was correct.  Am i on the right track?

[Dan]

2. How could you get an alcohol from an ester?

For this one i would say do the same thing i wrote on my answer sheet above^ .  I thought making a salt and alcohol was correct.  Am i on the right track?

Yes, but your mechanism is not right. The O that ends up in the alcohol should be the O bonded to the alkyl group in the ester- and the O from the hydroxide should end up in the salt. The idea is good though - ester hydrolysis (in base) gives an alcohol and a salt. So which ester do you want in order to get you desired alcohol?

[matt1234]

Im a little confused at this point, i thought the alcohol i would need is phenylmethanol?

Heres what i know:

carboxylic acid + alcohol = ester + HOH  (in a condensation rxn.)


Heres what i need to do:

ester + ?  =  aldehyde + (?)  

[Dan]

You're right, phenylmethanol (also called benzyl alcohol) is the alcohol you need, and you are correct that an ester + NaOH ---> carboxylate salt + alcohol - it was the specifics of this reaction that aren't quite right in your original picture (see below), but the overall product is correct.

The question is

ester + NaOH ----> salt + phenylmethanol (benzyl alcohol) --Ox--> Benzaldehyde

Which ester could you use?