Sciencemadness Discussion Board - Oxidation of Benzyl Chloride

Oxidation of Benzyl Chloride

Ieshwar - 28-9-2008 at 03:27

Hiya!

I'm Ieshwar. New to this forum. i had a few questions to ask .

I got a technical report to write about preparation of benzoic acid by oxidation (from benzyl chloride).

C6H5CH2CL + H20 -> C6H5CH20H + HCL
3 C6H6CH2OH + 4 MN04- -> 3 C6H5COO- + 4 MN02 + OH- + 4H2O
hydrated NAS AND HCL IS ADDED:
MN02 + SO2 -> MN2+ + SO42-
C6H5COO- + H2O + SO2 -> C6H5COOH + HSO3-

I know the first step/equation. It occurs without heating. right? I think na2co3 will be as catalyst. Will it?

Can you just explain the last 3 steps to me, with the conditions for industrial process? Or show me to a site where I can get more information? I have absolutely no idea. I've been looking on net since yesterday, all I get is a serious head ache! Please, help me out.

Thanks!

take care,
Ieshwar

Klute - 28-9-2008 at 05:41

In acidic conditions, you will not get MnO2, but soluble Mn 2+. Unless you isolate the benzyl alcohol before oxidation?

Because the second oxidation step is described in neutral/basic conditions (neutral becomes basic as the oxidation produces OH-)

If the reaction is performed in acidic conditions, the formed benzoic acid will precipitate, if you stay in neutral/basic it will be under the carboxylate form as described in your second equation.

In that case, addition of the sulfite (NAS? That isn't a correct term) will form a soluble sulfite compound (but you can simplify to Mn2+). this dissolve the thick, black deposit of MnO2 formed during the oxidation, and ables you to isolate your product without loosing some of it during filtration.

The last step is acidfying your formed carboxylate abck to an acid, which precipitates out, and can be filtered off. But it isn't the SO2 that acidifies the acid, it is HCl (H3O+ is much stronger than H2SO3). Be carefull though, you will have SO2 gas evolving from acidification of the sulfite.

This is why most of the time, when formingacids via KMnO4 oxidation, the MnO2 is filtered before hand, and then the excess MnO4- (pink colour) is neutralized with a few drops of sulfite.

Concerning the industrial conditions, I will let you do your homework. Check out various books, or just think about the steps and what you ahev learnt in school. Is this an exothermic reaction? Is a solid formed? Is a gas formed?

I suppsoe this is from the old industrial process where benzene is chloromethylated, and the formed benzyl chloride convert to various usefull products. There will be a lot of old patents lying around, that will surely give you details on the industrial application. Have a search in this forum, oxidation of xylenes to phtalic acids have been discussed and use the same conditions.

Nicodem - 29-9-2008 at 01:11

Ieshwar, Na2CO3 is not a catalyst. It is used as acid scavenger for the HCl formed during the hydrolysis of benzyl chloride. The reaction does occur without heating but not at an useful rate. It also requires very good stirring or at least a cosolvent. See the thread by Len1 about the hydrolysis of benzal chloride in Prepublication section - it is an analogous reaction.

Quote:

Originally posted by Klute
I suppsoe this is from the old industrial process where benzene is chloromethylated, and the formed benzyl chloride convert to various usefull products. There will be a lot of old patents lying around, that will surely give you details on the industrial application.

No, I don't think that is taken out of an actual process. I think he just combined a few equations from separate processes together without thinking much. Benzyl chloride, just like toluene, can be oxidized to benzoic acid directly with KMnO4. The hydrolysis to benzyl alcohol is quite obsolete.

Ieshwar - 29-9-2008 at 04:27

Quote:

Originally posted by Klute
In acidic conditions, you will not get MnO2, but soluble Mn 2+. Unless you isolate the benzyl alcohol before oxidation?

Perhaps, as Nicodem said, the Na2co3 will remove all the acid, making the medium neutral.

Quote:

In that case, addition of the sulfite (NAS? That isn't a correct term)

OOPS!

Quote:

will form a soluble sulfite compound (but you can simplify to Mn2+). this dissolve the thick, black deposit of MnO2 formed during the oxidation,

But according to the equation, it's so2 (where does it come from?) that dissolves the mn02. Any idea?

Quote:

Concerning the industrial conditions, I will let you do your homework. Check out various books, or just think about the steps and what you ahev learnt in school. Is this an exothermic reaction? Is a solid formed? Is a gas formed?

I suppsoe this is from the old industrial process where benzene is chloromethylated, and the formed benzyl chloride convert to various usefull products. There will be a lot of old patents lying around, that will surely give you details on the industrial application. Have a search in this forum, oxidation of xylenes to phtalic acids have been discussed and use the same conditions

Thanks!!!

Nicodem:

Quote:

The reaction does occur without heating but not at an useful rate. It also requires very good stirring or at least a cosolvent.

Oh. Ok. But any idea what temperature?

Quote:

Grrr! I'm sure she did it intentionally. to make our life miserable.

Thanks to both you! Huge thanks!!! Now, all these are starting to make a little bit of sense!

Take care,
Ieshwar

Klute - 29-9-2008 at 09:04

Acidified sulfite will give off SO2, no adding sulfite and acid simultaneously might act as dissolved SO2, btu much will be lost and bad choking SO2 fumes will be emmited... Check the phtalic acid thread for details on the oxidation of xylenes to the corresponding diacids with neutral KMnO4.

Reference Information

solo - 29-9-2008 at 09:19

Benzylic oxidation and photooxidation by air in the presence of graphite and cyclohexene
Grigoriy Sereda and Vikul Rajparaa
Tetrahedron Letters Volume 48, Issue 19, 7 May 2007, Pages 3417-3421

Abstract
Graphite is introduced as a convenient catalyst for cyclohexene-promoted photooxidation of p-xylene, ethylbenzene, and cumene by air. Availability of the reagent (air), lack of chemical waste, low toxicity, and reusability of the catalyst make the process a good green alternative of oxidation of these industrially important hydrocarbons.

Attachment: Benzylic oxidation and photooxidation by air in the presence of graphite and cyclohexene.pdf (122kB)
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Nicodem - 30-9-2008 at 01:55

Quote:

Originally posted by Ieshwar
Perhaps, as Nicodem said, the Na2co3 will remove all the acid, making the medium neutral.

The Na2CO3 is used in the benzyl chloride hydrolysis step, not in the benzyl alcohol oxidation.

Quote:

But according to the equation, it's so2 (where does it come from?) that dissolves the mn02. Any idea?

Sodium sulfite is only used to quench the oxidation and remove the insoluble MnO2 which can be a pain to filter. It does not have any role whatsoever in the oxidation reaction.

Quote:

Oh. Ok. But any idea what temperature?

Has it ever occurred to you to check the literature for the actual process of benzyl alcohol to benzoic acid oxidation? Nobody here is paid to do literature searches for you. If you want us to help you, first show that you did at least the minimum effort to find the answer yourself. You did not bother giving any reference for your claims and equations and now you expect us to do so for our claims? That is considered quite arrogant here around.

Ieshwar - 1-10-2008 at 07:09

Quote:

Originally posted by Klute
Acidified sulfite will give off SO2, no adding sulfite and acid simultaneously might act as dissolved SO2, btu much will be lost and bad choking SO2 fumes will be emmited... Check the phtalic acid thread for details on the oxidation of xylenes to the corresponding diacids with neutral KMnO4.

Thanks!! I'll check the thread, the next thing.

Quote:

Benzylic oxidation and photooxidation by air in the presence of graphite and cyclohexene
Grigoriy Sereda and Vikul Rajparaa
Tetrahedron Letters Volume 48, Issue 19, 7 May 2007, Pages 3417-3421

Abstract
Graphite is introduced as a convenient catalyst for cyclohexene-promoted photooxidation of p-xylene, ethylbenzene, and cumene by air. Availability of the reagent (air), lack of chemical waste, low toxicity, and reusability of the catalyst make the process a good green alternative of oxidation of these industrially important hydrocarbons.

Ah thanks! Really nice of you to find the reference.

Quote:

Sorry. I didn't mean to do that. I admit I was wrong. Sorry.
In fact, I did look into the net. But the information I got didn't tally with the equations that the lecturer had given us. Like, in one case, it was explaining how to oxidise benzyl chloride using h2o2. Oh well.
In fact, I'm in my first week into undergraduate. I have done phenols and benzoic acid in A levels, but benzyl alcohol and chloride are rather unfamiliar to me. I looked it up on the net. I found that the structure of alcohol one was similar to phenol. But wasn't sure about the chemical properties. But thanks to you guys, it's clearer now. With your help, I'm able to understand the paper better and also do my future research with a clearer view.

Thanks! And i'm really sorry to have come across as an arrogant. It wasn't my intention.

Take care.
Ieshwar

Nicodem - 1-10-2008 at 23:23

No problem... I think most members here would surely like to help you understand better the issues in your learning process that trouble you. However, you are now a student so you have to do your part of the learning process. The first thing you need to understand is that knowledge is hidden in the so called primary literature and unless you do your own literature search you will be full of misconceptions and misinterpretations of what you hear from second hand sources like professors or school books. "I looked it up on the net" is the worst you can do. The best thing you can do is search the primary literature using publishers search engines or go to the library to use Beilstein, SciFinder or Gmelin to get the references and then check the original papers. You should limit yourself to review papers at the beginning. For less problematic issues you can rely on books which you will have to read anyway. For organic chemistry you will have to read Vogel's for the practical chemistry and March's for mechanistic chemistry (these are the basic ones for undergraduates).
Hopefully you will soon learn that benzyl alcohol is not similar to phenol. The concept of similarity has its limitations and that's why we have categories like alcohols and phenols and only the most fresh beginners are allowed to view phenols as alcohols and even in such case preferably as "aromatic alcohols".