Mesa - 6-3-2014 at 01:34
I attempted to prepare benzaldehyde today, using a variation of the rather well discussed calcium hypochlorite method.
I'm posting this thread in the Beginner's forum because I cannot locate the reference I used for the procedure itself. The specific quantities of
reagents/substrate are sourced from said reference(3g Ca(OCl)2 in 50ml H2O/3g BzOH in 5ml CH3COOH were the exact quantities used in the paper)
The closest google results I could get to aforementioned paper are these:
http://www.sciencedirect.com/science/article/pii/S0040403900...
https://www.erowid.org/archive/rhodium/pdf/thf2gbl.ca-hypo.p...
Anyhow...
My aim was to observe how the reaction procedes, not to isolate the end product. I havn't seen lithium hypochlorite mentioned in any of the papers
regarding the oxidation of benzylic alcohols with hypochlorite salts, nor any hint as to why they would be excluded, so I ran the reaction myself with
the substituted hypochlorite. I used a slightly higher concentration of LiClO than that specified(LiClO mol weight is 58g/mol, Ca(OCl)2 mol weight is
140g/mol, I assumed 2 equiv LiClO would result in the same amount of hypochlorite ions in soln.)
Procedure was as follows:
I dissolved 3.5g LiClO(pool shock) in 50ml H2O with some difficulty in a 250ml beaker. I then added 3g of tech grade benzyl alcohol to 5ml glacial
acetic acid, and dripped it slowly into the hypochlorite soln. with stirring.
I noticed as the alcohol was being added, it would immediately form a white cloud of precipitate, which dissolved after a few seconds. I hadn't seen
any others report this occurance so I was a tad confused, an organic layer eventually formed with the characteristic smell of benzaldehyde. After
about half the alcohol/GAA was added, the cloudy precipitate stopped dissolving in the solution and remained suspended in the aqueous layer. I
stopped addition at this point and put the beaker aside.
An hour later, the aqueous layer still retained its cloudiness, however it had turned a dull red color and a second, distinctly crystalline
precipitate had formed. The separation between the organic layer and aqueous layer had become far less distinct at this point, although the
benzaldehyde smell was still easily recognizable.
My questions are:
-What is the cloudy precipitate forming upon addition of the alcohol?
My first thought was that it was immediately being oxidized to benzoic acid, however I feel the reaction would have been far more exothermic/vigorous
if this were the case. Also, the smell of benzaldehyde is unmistakable, even with the residual chlorine odor.
-Why did the aqueous layer turn red?
I'm completely stumped here, my only thought is that the reduced Li salt could do this, except lithium chloride is white.
-Why did the reaction proceed so quickly?
It was my understanding that it takes some time for the reaction to get underway. However I noticed the benzaldehyde smell as soon as the first
drop's precipitate cleared up(about 5 seconds after I added it.)
Edits: Added ref's and corrected LiOCL-->LiClO
[Edited on 6-3-2014 by Mesa]
[Edited on 6-3-2014 by Mesa]
TheChemiKid - 6-3-2014 at 04:49
EDIT: Never mind, I read CH3COOH as CH3CH2OH.
[Edited on 3-6-2014 by TheChemiKid]