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Rhodium please clarify !
Rhodium:
Wacker oxidation of cyclohexene in the presence of Pd(NO3)2/CuSO4/H3PMo12O40
Marisa S. Melgo, Alexandra Lindner and Ulf Schuchardt, Applied Catalysis A: General, Vol. 27x, p. xxx (2004) - Article in Press
DOI:10.1016/j.apcata.2004.06.035
Abstract
The Wacker oxidation of cyclohexene to cyclohexanone, using the chloride ion-free catalytic system Pd(NO3)2/CuSO4/H3PMo12O40, was investigated at different air pressures, temperatures, and catalyst concentrations. The results show that this system is very efficient and highly selective. After 1 h of reaction at 80°C and an air pressure of 50 bar, a conversion of 80%, with a turnover frequency of 260 h?1, and a selectivity of more than 99% for cyclohexanone was obtained. Using aqueous hydrogen peroxide and no external pressure, the oxidation was more rapid, giving 80% conversion already after 30 min and 95% conversion after 60 min without the formation of any byproducts.
Dope_Amine:
Hi Y'all! Someone is willing to do research.
Perchloric Wacker
The improved wack was done by my favorite harry primate: Max the bonobo, and no joke, he seriously went ape-shit over the results. Not only was the molar % of Pd greatly reduced from previous times, but the amount of benzoquinone too was reduced which makes life a lot easier. As many familiar with the benzo-wack know, the work-up is equally as important as the rxn for a pleasant outcome, so please take note of those details below or Max will throw some poop at you.
Based on the improved wacker article on Rhod's page:
120 g safrole (.74 moles)
1.66 g Pd(OAc)2 (1 molar %)
72 g benzoquinone (90 molar %)
19 g 70% perchloric acid
440 mL acetonitrile
60 mL water
Pd(OAc)2 was stirred for 30 minutes (to ensure good dissolution) w/350 mL AcCN in a 3 neck 2 L rb. Benzoquinone was added (endothermic), the funnel washed with 50 mL AcCN, and the solution was allowed to stir until temp climbed back up to ambient (~1 hr). Perchloric acid was then gently poured in (.24 M at midpoint of saf. addition). Flask was fitted with a condenser (not really necessary) and an addition funnel with 120 g safrole dissloved in 40 mL AcCN. Addition was started at a healthy drip rate. The flask heated up within minutes, but no condensate was ever noted in the condenser. The flask was allowed to stir until it returned to room temperature (~2 hours).
Work-up:
The reaction mix was filtered through an inch of packed, solvent-wetted celite (makes filtration very easy). The filtrate was then poured into a 4 L separatory funnel and shaken with (.45 L conc. HCl + 200 mL brine + 800 mL water). This is then extracted with 600, 300, 200, and 100 mL DCM, taking very great patience to allow a full as possible separation and with light agitation as it drains to knock DCM globs to the bottom. Care was also taken to not allow the crud at the bottom edge of the water layer into the pooled DCM. The DCM was then washed once with 500 mL sodium bicarbonate. This is the main wash where product will be lost if not careful, so patience with the separation is very beneficial as well as maybe the addition of some brine (50-100 mL). One can check that they got most all of their product by making sure that the total pooled DCM adds up to close to 1200 mL (DCM) + 110 mL ('tone) + ~150 mL more DCM (used to wash the rxn flask, filter funnel, and filter flask) or, alternatively one could back extract with a bit of DCM. Next, the DCM/'tone is washed once with 500 mL brine and twice with 10% NaOH (again care and patience). The DCM/'tone is then dried with mag. sulfate and distilled (24/40 regular vac. distill set-up pulls faster and potentially with more theoretical plates than a short path). There is no noticable forerun of saf/isosaf, just straight bright neon-yellow/clearish 'tone (118 g) and a bit of black crap left in the flask. Yield: 89.5% The H'nMR looked very good, very clean.
If only ya didn't have to do the washes, I think this modified wacker would get up to 95%. Might asarone do as well or would the perchloric acid cause some issues? Hmmm.....
Dope_Amine:
It depends on your vac. Max's is somewhat crappy right now so it came over at ~130 +/-5 °C
These questions are kinda more dependant from person to person and since I think you are mostly going to ask q's that only serve you, I think pm is the best way to converse. Reduce the crap that peope have to filter when going through TFSE ya know.
Anywayz, typically if you have good 'tone, it is yellow. Double distilled 'tone is clear. So, clear-ish/yellow 'tone from the first distillation would bee a good sign. During distillation, normally with the regular benzo wack, one gets a few mL's of completely clear isosaf b4 the temp climbs a bit and the 'tone comes over.
Not the case with the perchloric version.... :P
bbeeasheets:
from the workup
"The filtrate was then poured into a 4 L separatory funnel and shaken with (.45 L conc. HCl + 200 mL brine + 800 mL water"
does this mean all at once? or each of those separately? i know this is a stupid question, but .....i am new after all!
i am planning on testing this thursday....since my performics appear to suck on yields
thanks for the awesome research Dope_Amine!
Dope_Amine:
Yea, all at once.
One of the biggest problems with the benzo wacker is the work-up. It can totally fuck your yields. I absolutely do not recommend trying to scale up the 'tone without scaling up the washings also. What is stated is barely enough to get it well clean enough for a good distillation- mainly refined by doing extra washes and realizing that they didn't do all that much. In the future, it might bee decided to get rid of the bicarb wash altogether, cuz that's a real motherfucker on da yield.... Prolly, next time it'll bee dropped and we'll see how it goes. If you wanna give it a try, then get rid of the bicarb wash and maybee do an extra brine wash or maybee not. Then let us know. Otherwize, we'll have to wait a while for the bonobo to do it (he's a busy primate). :P
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