Or it's diethyl acetal, at least.
Here is an Idea, and a request for comments.
Basically, the usual problem with producing acetaldehyde is twofold. One, normal oxidizing agents tend to overoxidize the aldehyde to acetic acid, which is not what we want. This can bee partially overcome by continuous distillation of the formed aldehyde. Two, acetaldehyde has a very annoyingly low boiling point, which requires it to be stored in some other form, like paraldehyde, an ammonia adduct, etc.
My proposal attempts to solve both problems at once, with no distillation.
The idea is basically this. Into a room-temperature solution of HCl in ethanol is introduced dropwise 1/4 equivalent bleach or strong NaOCl or Ca(OCl)2 solution. The after the addition ends, the solution is stirred for 30 minutes, then diluted with cold water, and the top layer of acetaldehyde diethyl acetal removed.
When the acetaldehyde is desired, it can be hydrolyzed from this acetal form, or, more likely, used as it is.
The following reactions should occur:
Acidic bleach equilibrium tends to the right:
NaOCl + HCl <--> NaCl + HOCl, + HCl <--> H2O + Cl2
Oxidation of alcohol to aldehyde regenerates the 2 HCl
CH3CH2OH + Cl2 --> CH3CH=O + 2 HCl
The aldehyde, in the presence of HCl and excess ethanol, forms an acetal immediately, which is resistant to further oxidation.
CH3CH=O + 2 CH3CH2OH --> CH3CH(OEt)2 + 2 H2O
If need be, a drying agent can be used to remove water from the alcohol layer, but I suspect the NaCl generated by the oxidation is going to pull out the water (salting out) from the alcohol layer as is. More salt could always be added to begin with.
(1 NaCl is generated for every 3 H2O)
By adding the oxidizing agent slowly, we ensure that the formed aldehyde immediately meets more ethanol, to prevent the other two undesireable reactions from happening:
1. acid catalyzed alpha-chlorination
CH3CH=O + Cl2 --> ClCH2CH=O + HCl
2. oxidation of hemiacetal or hydrate form.
CH3CH(OH)OR + Cl2 --> CH3CH(=O)OR
By means of this careful operation, I expect high yields.
The extraction takes advantage of the fact that while we could distill the alcohol off the acetal, it shouldn't be necessary, due to the widely differing solubilities of the two compounds in water. AFAIK, acetal is not soluble in water much, like ether. That being the case, simply diluting the product should cause the acetal to separate, if it hasn't already.
This seems to be the easiest, simplest, least apparatus-intensive way to get decent yields of acetaldehyde.
A THEORETICAL EXPERIMENT
75 g commercial Ca(OCl)2 is slowly added with stirring to 150 ml 95% ethanol acidified to pH 1 with concentrated HCl. The mixture is stirred for an hour as addition progresses, and for 30 minutes after it is completed. At this point, the mixure may have separated into two layers, or not. The mixture is filtered and poured into 100 ml ice-cold water, and the water layer stripped off in a separatory funnel. The acetal may be dried over CaCl2 or left as-is.
Thoughts?