(Official Hive Translator)
Double bond ox. cleavage (to aldehyde) with CuO
(Rated as: excellent)
This is from the same source that the preparation of 3,5-diMeO-4-OH-propenylbenzene, which i recently posted into Methods discourse - see Post 293193 (Antoncho: "2,6-diMeO-4-allylphenol", Methods Discourse).
Edit: the original info comes from Patent US2516412
I'm not sure if this hasn't been discussed bee4 - i just couldn't construct an accurate query on TFSE. But i think it hasn't since - why then no one ever thought of possibility of applying this to piperic acid?
EXAMPLE VII: Syringaldehyde from the isolated intermediate
Syringaldehyde may also be prepared by oxidizing the isolated 3,5-dimethoxy-4-hydroxypropenylbenzene of Example V with nitrobenzene in alkali or other low potential oxidizing agents.
Thus 195 parts 3,5-dimethoxy-4-hydroxypropenylbenzene are added to a cupric oxide mixture freshly prepared from 1000 parts hydrated copper sulfate, 660 parts sodium hydroxide, and 8000 parts of water and the resulting mixture is
heated to boiling under reflux for eight hours. The separated red cuprous oxide is filtered and washed with water. The alkaline filtrate and washings are acidified and extracted with ether.
Bisulfite purification of the ether extract should yield approximately 155 parts or 90% syringaldehyde.
Other alkaline copper oxidizing agents such as Fehling's Solution, Benedictís Solution, may be used with the same results. An alkaline copper oxidizing agent is particularly advantageous for replacing the propenyl group with the aldehyde group because the strength of its action in changing from a cupric to a cuprous compound is definitely adequate to oxidize to the aldehyde, and at the same time insufficient to continue the oxidation to the acid further or to destruction. However, in large scale operation, it will be obvious that oxidizing agents having no such automatic action may be employed for reasons of economy, and the extent of the reaction controlled by controlling the amount of the reagent.
So... What do you think?
One thing that confuses me is - AFAIK, Fehling's liquid is a Cu++/NH3 complex - which will certainly decompose at 100 C, with all ammonia going out of solution. What could they mean?
why then no one ever thought of possibility of applying this to piperic acid? Nice thought Could it work?
here's another one, using potassium permanganate and easy work-up. otto is not sure wether this has been discussed before:
Synthesis 2001, No.11, pp 1645-1648
"Heterogenous Permanganate Oxidation of Styrene and Cinnamic Acid Derivatives: A Simple and Effective Method for the Preparation of Benzaldehydes"
Abstract: Styrene and cinnamic acid derivatives yield correspondingly substituted benzaldehydes when oxidized by permanganate under heterogenous conditions...Alumina and Amberlite IR-120 can be used as solid supports in these reactions with equally good results.
typical procedure (anisaldehyde):
to a solution of anethole (0.148 g, 1 mmol) in DCM (35 ml) was added KMnO4/alumina reagent (4.65 g, preparation by combining 0.78 g KMnO4, 3.12 g Al2O3 (acidic, Brockmannn I) and 0.78 ml H2O and grinding in a mortar until homgenous ~3min). the heterogenous mixture was stirred at r.t. until TLC indicates completion (4h). the contents of the flask were filtered through celite and washed with DCM (3*15ml) product was sep'd by evaporation of the solvent to give 94% yield of p-anisaldehyde (0.128 g).
cinnamic acid-->benzaldehyde 90%
3bromocinnamic acid-->3bromobenzaldehyde 99%
2hydroxy cinnamic acid-->salicylaldehyde 85%
and so on (28 entries)
benzylic double bonds to benzaldehydes
(Rated as: excellent)
Here is another procedure that should definately give piperonal from piperine. It also gives benzaldehyde from cinnamaldehyde.
Bis(2,2'-bipyridyl)copper(II) permanganate (BBCP): A mild and versatile oxidant in organic synthesis
Tetrahedron, Volume 40, Issue 23, 1984, Pages 5001-5004
H. Firouzabadi, , A. R. Sardarian, M. Naderi and B. Vessal
The preparation of bis(2,2'-bipyridyl)copper(II) permanganate (BBCP) is described. The reagent converts alcohols to the corresponding carbonyl compounds, -hydroxy ketones to diketones, hydroquinone to p-benzoquinone, and compounds with benzylic double bonds to benzaldehyde in high yield. Benzophenone oxime, acetophenone oxime and various benzaldoximes are converted to the corresponding carbonyl compounds, aromatic amines to azo compounds, and benzylamine to benzaldehyde, usually in high yields, under mild condition.
To 2,2í-bipyridyl (0.02mol) in acetone-water (50/50),
solution of copper(II) chloride (0.01 mol) in water (25 ml)
was added with stirring. The dark blue solution was concentrated and cooled in an ice bath to produce crystals in quantitative yeild. (m.p. 250C w. decomp.)
To bis(2,2'-bipyridyl)copper(II) chloride (0.02 mol) in water (25 ml). Potassium permanganate (0.01 mol) in water was added with stirring. The dark purple solution was cooled
and the crystalline compound was collected and dried in air,(yield 95%; m.p.105-110c decomp.)
General procedure for the conversion of hydroxy compounds to their carbonyl compounds.
To the alcohol (0.01mol) in dry CH2Cl2 (50ml) in rbf equipped with a condenser and a mag. stirrer, oxidizing reagent (0.005-0.015mol) was added and stirred 0.25 to 3 hours at room temp. The rxn mix is filtered and solid material washed w. CH2Cl2. Filtrates are combined and evaped. Residue is chromatographed on silica gel, evap. of solvent affords carbonyl compound in 75-100% yeild.
General procedure for the oxidation of benzylic double bonds.
To the alcohol (0.01mol) in dry acetone (25ml) in rbf (50ml) equipped with a condenser and a mag. stirrer, oxidizing reagent (0.01mol) was added and stirred for 10 min. The rxn mix is filtered and solid material washed w. acetone. Filtrates are combined and evaped. Residue is chromatographed on silica gel, evap. of solvent affords carbonyl compound in 80-95% yeild.
Table 1:Oxidation of various organic compounds with BBCP
Benzyl Alcohol to Benzaldehyde; Time(hr) 0.25; yeild 95%; Oxidant/Reactant 0.5
Benzyl Alcohol to Benzaldehyde(a); Time(hr) 4; yeild 20-30%; Oxidant/Reactant 0.5
Benzhydol to Benzophenone; Time(hr) 0.5; yeild 100%; Oxidant/Reactant 0.5
Furfuril Alcohol to Furfural; Time(hr) 0.3; yeild 90%; Oxidant/Reactant 0.5
9-Phenanthrene-methanol to 9-phenanthrene-carboxaldehyde; Time(hr) 0.9; yeild 95%; Oxidant/Reactant 0.5
Citronellol to Citronellal; Time(hr) 1; yeild 75-83%; Oxidant/Reactant 0.75
Cinnamyl Alcohol to Cinnamaldehyde; Time(hr) 1; yeild 95%; Oxidant/Reactant 1.5
Cinnamyl Alcohol to Benzaldehyde(a); Time(hr) 0.5; yeild 80%; Oxidant/Reactant 1.5
Cinnamyl Alcohol to Benzaldehyde(b); Time(hr) 0.5; yeild 90%; Oxidant/Reactant 1.5
Furfuril Alcohol to Furfural(b); Time(hr) 0.1; yeild 100%; Oxidant/Reactant 0.5
Mandelic Acid to Benzaldehyde(b); Time(hr) 0.5; yeild 90%; Oxidant/Reactant 0.5
p-Nitrobenzyl alcohol to p-nitrobenzaldehyde; Time(hr) 1.5; yeild 90-100%; Oxidant/Reactant 0.75
Hydroquinone to Benzoquinone; Time(hr) 0.25; yeild 100%; Oxidant/Reactant 0.5
Piperonol to Piperonal; Time(hr) 0.5; yeild 100%; Oxidant/Reactant 0.5
C6H5CHCHC(O)C6H5 to Benzaldehyde(b); Time(hr) 0.25; yeild 85-90%; Oxidant/Reactant 1
C6H5CHCHC(O)CH3 to Benzaldehyde(b); Time(hr) 0.25; yeild 80-90%; Oxidant/Reactant 1
C6H5CHCHC(O)H to Benzaldehyde(b); Time(hr) 0.1; yeild 80-85%; Oxidant/Reactant 1
(a) Reactions performed in water
(b) Reactions in acetone
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