Sciencemadness Discussion Board

shameless spoonfeed

arkoma - 1-12-2018 at 09:01

My TEMPO ought be here Monday. Already have CuCl2 and Benzyl alcohol. These damned research papers make my old redneck eyes cross.

Project parameters anyone?

Yes, benzaldehyde desired end product.

Also have 95% EtOH--Acetaldehyde possible?

Tsjerk - 1-12-2018 at 09:45

Are you trying to find a procedure utilizing only copper and TEMPO? Because I cant find one that doesn't use some other non-OTC catalysts.

DavidJR - 1-12-2018 at 09:58

Why not make/get some pyridinium chlorochromate if you want to make aldehydes?

Tsjerk - 1-12-2018 at 11:28

Because he bought TEMPO from Melgar.

Tsjerk - 2-12-2018 at 04:10

@arkoma; do you have a DOI of an article describing the reaction you are pursuing?

Something like this? Did you get the TBAB from Melgar as well?

https://sci-hub.tw/10.1021/ol005792g

Oxone and DCM are OTC in the States aren't they?
Quote:

(19) Representative procedure: To a solution of the alcohol (1 mmol)
and Bu4NBr (4 mol %, 0.04 mmol) in 5 mL of the indicated solvent is
added TEMPO (1 mol %, 0.01 mmol, 0.1 M solution of the indicated
solvent) and Oxone (2.2 equiv, 2.2 mmol). The mixture is then stirred for
12 h at room temperature, and the reaction is monitored by TLC. After the
reaction is complete, the solvent is removed under reduced pressure, and
the remaining solid is purified by column chromatography (silica gel,
hexanes/ethyl acetate: 10/1).

If TLC is difficult you can just close the reaction vessel from atmospheric oxygen (benzaldyde oxidizes with oxygen) and run the reaction for 24 hours or so, I don't think this will lower the yield.

I guess the purification could be done through bisulfite.

[Edited on 2-12-2018 by Tsjerk]

[Edited on 2-12-2018 by Tsjerk]

CuReUS - 2-12-2018 at 08:41

https://pubs.acs.org/doi/10.1021/ja00323a064

WGTR - 2-12-2018 at 10:23

Well, you could make bezaldehyde from benzyl alcohol and copper if you were willing to tackle building a small tube furnace. Sabatier apparently did this, and briefly reported results on page 235 (section 657) of Catalysis in Organic Chemistry:

http://library.sciencemadness.org/library/books/catalysis_in...

It's necessary to read the whole chapter to gain the proper experimental context. Section 655 discusses how catalyst preparation conditions affect its activity. High surface area copper is too active for producing formaldehyde or an aromatic aldehyde like benzaldehyde, and causes them to decompose further to lower products. Lower surface area copper is better for something like these.

Copper oxide is interesting in that it is very easy to reduce it to elemental copper with organic vapors at relatively low temperatures (under 200°C in some cases). If you've ever tried to machine copper, you've noticed that clean, hot, copper easily sticks to itself. This can make it difficult to obtain a clean finish on the workpiece. In a reducing environment of alcohol vapors, high surface area copper slowly sinters together. This effect can be slow at 200°C, but rapid at 400°C. This is true even though the temperature is far below the melting point of copper. Reduced copper that is prepared with alcohol vapors slowly at 200°C will tend to have high surface area, with a characteristic violet coloration. If prepared at 400-500°C, the lower surface area product should have a coloration more characteristic of copper. It is the low surface area product that you would want for benzaldehyde production, in my understanding. You might even be able to get away with just using a hot copper tube.

Conversion from the alcohol probably wouldn't be 100%, and if the temperature goes too high you could apparently have some benzene and toluene in the product. If you have some distillation equipment to separate out the products it might be something fun to try, though. Another option might be to form a bisulfite adduct to separate out the aldehyde, but I don't have much experience with that.

If I was the one trying it, I'd probably bubble some nitrogen through hot benzyl alcohol, to pick up the alcohol vapors. The nitrogen would help drive the reaction to completion, by diluting out the hydrogen in the product. Another option, as mentioned in the book, is to run the reaction under vacuum to the same effect. Failing that, the reaction should still work at atmospheric pressure without a carrier gas or vacuum, it would just be necessary to separate out the aldehyde product from a considerable amount of unconverted alcohol.

I've never tried making benzaldehyde this way, but I've made some small amounts of acetaldehyde using a tube furnace.

SWIM - 2-12-2018 at 10:51

That thread tittle made me assume this was another weird porno spam post.

Glad to see it's good clean chemistry.

arkoma - 2-12-2018 at 18:45

On my mobile. Yes, oxone and dcm otc here. Will read thread tomorrow on laptop! And yueld ain't important-spent all day before on a dab of methyl salicylate

weilawei - 2-12-2018 at 19:26

Sabbasani Rajasekhara Reddy , Selvaraj Stella & Anju Chadha (2012)
Simplified Procedure for TEMPO-Catalyzed Oxidation: Selective Oxidation of Alcohols, α-HydroxyEsters, and Amides Using TEMPO and Calcium Hypochlorite, Synthetic Communications, 42:23,3493-3503, DOI: 10.1080/00397911.2011.584650
Quote:
Initial studies of oxidation were done using sodium hypochlorite as an oxidant(1mmol) and a catalytic amount of TEMPO (0.01mmol) without additives.At thepH of commercial bleach (12.7), oxidation of p-methoxy benzyl alcohol gave the cor-responding aldehyde only in 43% yield after 3h.Whelcium hypochlorite wasused as an oxidant under identical conditions, to our delight the reaction was com-plete in 1h and gave p-methoxy benzladehyde in 92% isolated yield.The pH of theoxidation reaction was nearly neutral.Possibly, the generated acid (Hþ) [Ca(OCl)2reacts with water to produce HOCl and (Ca(OH)2); and the available chlorine(65%) in Ca(OCl)2reacts with water to produce HOCl and HCl] is neutralized bya base (Ca(OH)2(pKb–2.43),[8]thereby making the reaction condition mild and suit-able for various functional group tolerance.Further, when the oxidation of p-meth-oxy benzyl alcohol was done with oxidant Ca(OCl)2in the absence of TEMPO, onlya trace amount of the product was observed.The catalyst TEMPO is important forthe reaction to proceed, and the mechanism of TEMPO in alcohol oxidation hasbeen well discussed in previous papers.[1d,4g,5h]

The generality of the TEMPO–calcium hypochlorite catalyst system was exam-ined by the oxidation of a wide range of alcohols.Benzylic alcohols and its derivativesgave excellent yields of the products (85–97%) (Table 1, entries 1–4).Allylic (entry 14),cyclic (entry 10), and nonbenzylic (entry 5) alcohols were also selectively oxidized tothe corresponding aldehydes and ketones in moderate to excellent yields (60–85%).


Edit: Is anyone interested in a list of TEMPO references? I've collected a number of papers searching the literature, and I think they'd be handy to anyone doing experiments with it or related catalysts.

[Edited on 3-12-2018 by weilawei]