Close, but not quite. When TCCA dissolves in water, it forms hypochlorous acid HOCl. TEMPO is a funny thing, I think it is in fact an N-oxide, not your average PTC at all. I think TEMPO could bee substituted with pyridine N-oxide or triethylamine N-oxide, but good luck finding them either.
However, my understanding of how the oxidation proceeds is like this:
R-CH2-OH + HOCl --> R-CH=O + HOH + HCl
The problem is, the water can add like so to give a hydrate:
R-CH=O + HOH --> R-CH(OH)OH
Which, while reversible, is easily dehydrogenated once more:
R-CH(OH)OH + HOCl --> R-C(OH)=O + HOH + HCl
This is why chlorine anhydrous works -- when there's no water to form a hydrate, oxidation cannot proceed beyond the aldehyde stage (without forming an acid chloride, another matter entirely). Unfortunately, side reactions limit the usefulness of this.
This would bee one reason PTCs would work with some compounds. They could carry, for example, OCl- ion into a non-aqueous phase, where it could dehydrogenate alcohols to aldehydes, without the aldehydes being able to enter the water and form hydrates. Unfortunately, for lower alcohols and aldehydes which are well soluble in both polar and nonpolar solvents, I'm not so sure this technique will work.
In the above suggestion, TCCA is being used anhydrously as a dry chlorine substitute/source. Apparently acetaldehyde is formed in good yield from ethanol in the first step of chlorination of ethanol, followed by mono, di, and finally trichloroacetaldehyde. I guess this selectivity would be observed because the result of chlorination is HCl, which unlike bases causes further chlorination of alpha-chloro carbonyl compounds to become more difficult rather than easier. TCCA eats HCl to produce more chlorine, but since the reaction is a dehydrogenation it will tend to run away if not carefully controlled.
TCCA is very soluble in ethyl acetate and acetone (~370 g/L), which can be used to slowly introduce TCCA solution by dropping funnel into a heated flask of ethanol. With the acetaldehyde and HCl distilling over into a second flask of ethanol through bubbler, the HCl will soon saturate the solution and catalyze acetaldehyde polymerization, I guess.
I heard the ammonia adduct of acetaldehyde is good to purify it.
Organikum knows all about the method of dehydrogenating ethanol with copper/zinc catalyst. The science madness board has a lovely thread on this topic, complete with pics. It's very industrial.
However, I would like to see this one tried, since it seems much easier.
Stoichiometry:
TCCA has 3 active chlorines.
C3O3N3.Cl3 + 3 HCl + 3 CH3CH2OH --> C3O3N3H3 + 3 CH3CH=O + 6 HCl
As you can see, to just mix the reactants would be very careless and dangerous. Kaboom! If the TCCA is added seperately and measuredly, it should be safe.
Probably the best thing to do with you acetaldehyde gas is to use it immediately. Presumably you would be reacting it with methylamine. Use a bubbler or something, and if necessary, strip out the HCl gas with a base.
So that's 1/3 mole TCCA for 1 mole ethanol. 232 g TCCA for 138 g ethanol. I'd probably use an excess of ethanol for convenience. If the TCCA is dissolved in acetone, watch out for the probably inevitable chloroacetones that will be formed as side products. Then again, if an excess of acetone is used, it will raise yield of acetaldehyde by competing with acetaldehyde for alpha-chlorination. Conceivably, one could obtain both chloroacetone and acetaldehyde in the same reaction by this method.
So no, organikum, this is similar but not exactly the same as the standard TCCA oxidation. It's more like a chlorination. Those flocculators I don't know about. I know the algae killers contain typically alkyl (C12,C13,C14) benzyl dimethyl ammonium or alkyl trimethyl ammonium salts where I live. A good source of PTCs, in fact. Those PTCs are good for "hard" bases, i.e. hydroxide ion. Perfect for hardcore deprotonations and alkylations, like benzyl cyanide and acetoacetic acid ester condensation, or Dieckmann cyclizations. Maybe even isomerization of allylbenzenes. Those type of quaternaries can decompose at higher temperatures, particularly under strong base conditions, but certainly if I wanted to alkylate, say, ethyl N-methyl carbamate or methyl acetamide with some type of secondary bromide
, they are what I'd try first.
By the way, does anyone know if Na2CO3 is a strong enough base to break chloroform off of trichloroacetaldehyde? It's a lot cheaper than NaOH. Perhaps Ca(OH)2 is cheapest, but it's annoying to deal with.
