Author Topic: The easiest synth of benzaldehyde from toluene  (Read 60958 times)

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  • Guest
Crossposting, Hah!
« Reply #20 on: September 05, 2003, 08:52:00 PM »
(Hive Bee)
09-04-03 06:39
No 457114 
Post 457114 (not existing)

         synthesis of benzaldehyde

Water Science and Technology Vol 34 No 10 pp 113–120 © IWA Publishing 1996
A study on wastewater minimization in indirect electrochemical synthesis of benzaldehyde
Ding Zhou, Zhirong Sun and Wanli Hu

Department of Applied Chemistry, Harbin Institute of Technology Harbin, 15001 China

Development of methods of pollution prevention is a strategic orientation for environmental protection. This paper describes studies on waste minimization in benzaldehyde production by using indirect electrochemical oxidation of toluene instead of the seriously polluting traditional chemical process. The new technology developed eliminates the discharge of wastewater by recycling the reactive solution and gives a higher yield of benzaldehyde


Journal of Applied Electrochemistry  33 (3/4)   p.273-277  March 4, 2003    Kluwer

A new approach to electrochemical production of benzaldehyde from toluene in an undivided cell in the presence of the couple V5+/V4+
Qingfeng Y.1  Xiaoping L.2    and  Xiuling Z.2


Oxidation of toluene to benzaldehyde in the presence of the redox couple V5+/V4+ was carried out in an undivided cell where oxygen gas was continuously bubbled over the cathodic surface and the electrolyte was a mixture of aqueous H2SO4 solution containing V5+ and toluene. Some experimental conditions affecting the current efficiency for benzaldehyde production, such as H2SO4 concentration, current density, V5+ concentration and surfactants, were determined. The maximum current efficiency for benzaldehyde production at ambient temperature was 156.3% under the conditions of 11 M H2SO4, 2.7 × 10?4 M CTAB, current density 1.25 mA cm?2 and 0.0128 M V5+.
Kudos to Tdurden969 . LT/


  • Guest
>current density 1.25 mA cm?2 LabTop,
« Reply #21 on: September 07, 2003, 10:57:00 PM »
>current density 1.25 mA cm?2

LabTop, shouldn't cubic centimetres describe current density and not ^2?

Why is the reaction not producing better yields?
Is there any obvious improvements that could bee made by changing the conditions or adding more catalyst?

Don't expect a reply, heh it's too scary in these forums for now, I'm just interested.  ;)


  • Guest
« Reply #22 on: September 07, 2003, 11:31:00 PM »
> LabTop, shouldn't cubic centimetres describe current density and not ^2?

what are you talking about?
current is measured in A (or in this case in mA).
a density is amount per volume or surface. in this case it's current
per electrode surface. the electrode surface is measured in cm^2.
mA per cm^2 = ma / (cm^2) =^-2.

> Why is the reaction not producing better yields?

i have no idea which reaction you are talking about, but over oxidation
might be a good guess.


  • Guest
hypo I just didn't know that.
« Reply #23 on: September 08, 2003, 06:10:00 PM »
hypo I just didn't know that. I'm sure he knew I was just looking for clarification.
I was talking about the current density of the solvent and electrolite.

I was talking about the electrolysis, do you know how to improve the over-oxidation problem?
A reduction in the amount of H2SO4 maybee?


  • Guest
reaction to benzaldehyd by manganeseperasulfat
« Reply #24 on: September 09, 2003, 08:04:00 PM »
The thread shows a way to make benzald. from toluen by oxidation with Mn02. And some of you said that it won´t work well, because the Mno2 has to be "activaded". Here is a easy way to make it from Mn(v)sulfat. A way I used many time!
First get some Mno2. In Germany you can by it as "Manganese-Black" an Wallpaint-color-powder. Thats about 70% Mno2. Then put it in an equimolar amount of H2SO4 (100%) and heat it up. Make it realy hot. (>200°C). Let it be there for about half an hour. When I do this, I let The acid become so hot, that white steam comes out. After that, let it cool down. You just have maid Mn(V)SO4. It is soluble in 37% H2SO4 with a deep, chocolate like broun color.
After that put it 1:1 with the toluene in about 60% H2SO4(enough H2SO4, so that nearly everthing disolves). Heat (or cool) it to about 50-60°C and stear it well. After 3-4 hours youl will have mostly Benzaldehyd ( in my cases about 70%)
Destill the Benzaldehyd/Toluene out by a simple steam destilation. (Just cook some water out, until there is no oily layer any more)
Wenn you start cooking that stuff, the color of the liquid become sand-like. Thats why the rest of the Mn(V)SO4 breaks down to Mn(II)SO4.
And now the best: just put the liquid in a eloctro. cell(in the anode-part) and put some electricity through it, while stearing. The color will chance to chocolate broun once again, and you can use it again!!! About 6 times!

Hope I could help you!
As you see my english is PERFEKT! But i thought I had to help you....


  • Guest
« Reply #25 on: September 10, 2003, 02:10:00 AM »
Rhodium posted these references (Thanks!):

A new approach to electrochemical production of benzaldehyde from toluene in an undivided cell in the presence of the couple V5+/V4+ - (100+% efficency!)
Qingfeng Y.,  Xiaoping L., Xiuling Z.

Journal of Applied Electrochemistry 33(3/4), 273-277 (2003)


A study on wastewater minimization in indirect electrochemical synthesis of benzaldehyde
Ding Zhoua, Zhirong Suna and Wanli Hu

Water Science and Technology 34(10), 113-120 (1996)



I havent read through them just yet (just glanced - dinner), figured I'd let ya'all who don't check the Ref thread know.



  • Guest
Just another oxidiser - Manganese-(III)-sulfate
« Reply #26 on: September 14, 2003, 04:12:00 PM »
Process for the preparation of an oxidiser:

The process implies the dissolution of manganese-IV-dioxide in sulfuric acid of 50-60% strength in the presence of manganese-II-sulfate. To obtain the oxidiser as a solid, a cold saturated solution of manganese-II-sulfate in water is prepared and concentrated sulfuric acid is added (with cooling, of course) until the solution contains 50-60% sulfuric acid.
The purpose of precipitating the manganese-(II)-sulfate by addition of sulfuric acid is to get the sulfate in finely divided particles, but finely ground manganese-(II)-sulfate could also be used with the same results.
To the crystalline sludge such obtained an equimolar part of manganese dioxide is added under strirring, i.e. for 1 Mol MnSO4 1Mol MnO2 is added. The slush is stirred until the manganese dioxide has dissolved under warming (the reaction is exothermic).
On cooling or upon addition of more (cold) concentrated sulfuric acid the oxidiser settles out in the form of lustrous, brown-red needles.
The product such obtained can be dissolved in organic acids, like acetic acid, and can be used in such solution to react with dissolved organic compounds which otherwise would be destroyed by concentrated sulfuric acid.
The oxidiser itself remains unchanged in its solid form if all traces of water are excluded.

[Translated from:  D.R.P. 205200, titled "Verfahren zur Herstellung eines Oxidationsmittels"]

Italics mine

The reaction involved in this process is:
MnO2 +MnSO4 +2H2SO4 --> Mn2(SO4)3 +2H2O

The preparation of this compound is comparable to the prep. of Mn-(IV)-sulfate, as described by neograviton, but the need of working with fuming hot sulfuric acid is omitted, which seems to be a little healthier... :)
Also, like in neograviton's preparation, there is no need for purchasing watched items like potassium permanganate for the preparation of activated manganese dioxide  ;)

An educated guess at last:
For the preparation of benzaldehyde from toluene, I think the procedure described by neograviton should work equally well with the use of abovementioned Mn-(III)-sulfate, there is even no need of isolating this compound from the 60% sulfuric acid solution, use it as it is.


  • Guest
You can activate MnO2 by impregnating it with HNO3
« Reply #27 on: October 30, 2003, 11:50:00 PM »
Or by heating at 110-125 degrees for 24-52 hours in a stove.
Both might work.
Have read some papers on that.
Seems MnO2 is a real touchy one...
Ning thinks that drying the stuff is kind of a waste if you are plunking back into water, as ning is. The nitric acid bit might not be so hard to do, though.
More details when time avails.


  • Guest
An easier way?
« Reply #28 on: October 31, 2003, 01:42:00 AM »
Has anyone ever tried Fe(II) (perhaps with Cu(II)?) and H2O2 (perhaps with H+) on toluene? This would be a completely OTC approach that would be very practical... of course getting to benzaldehyde is only part of the struggle.

Catalytic H2O2 with copper, iron, manganese or a bunch of other transition metal compounds is well known chemistry so perhaps the info is already out there... this would be a fundamentally awesome synthesis.


  • Guest
I've thought about the possibility of ...
« Reply #29 on: November 01, 2003, 11:28:00 AM »
I've thought about the possibility of replacing peroxodisulfate with H2O2 too. It turns out that the reaction is based on the reduction of peroxodisulfate ion by a metal ion to sulfate radical and a sulfate ion. The sulfate radical is the species that abstracts an electron from toluene forming toluene radical cation thusly starting the oxidation. Analogically hydrogen peroxide is reduced into hydroxyl radical and a hydroxyl ion, but the hydroxyl radical is electrophilic and reacts with toluene forming a hydroxycyclohexadienyl radical which most likely results in the formation of a phenols, so getting good yields of benzaldehyde from toluene isn't likely to happen. :(

By the way, in the patent (

Patent US4146582

) they say that acetic acid, for one, is a "particularly suitable organic solvent" for the reaction, but according to literature the yields are going to be lower due to formation of benzyl acetates. Typical of patents. They also say nothing about the ratio of methanol and water used in the persulfate solution... maybe the point is to use the same ratio as in the reaction mix.

J. Chem. Soc. Abstracts 1963, 2897-2905
J. Am. Chem. Soc. 97(2), 363-365 (1975)
J. Org. Chem. 48(25), 4910-4914 (1983)
Synthesis 1980, 477-479
J. Am. Chem. Soc. 106(24), 7573-7578 (1984)
Tet. Lett. 22(27), 2605-2608 (1981)


  • Guest
« Reply #30 on: November 17, 2003, 03:03:00 PM »

Patent US6495726

Chromic this patent uses air, toluene and cheap metal catalyst such as salts of Fe and Mn or Cu.

tdurden posted the same one i see, but it's relevent to your thoughts in case you forgot to read it.

The present invention relates to an improved process for the production of benzaldehyde with 40-50% selectivity comprising by catalytic liquid phase air oxidation of toluene. The process involves providing a continuous flow of air in the presence of a catalyst such as salts of Fe, Co, Mo and Ni, and preferably a co-catalyst such as salts of manganese or copper, a promoter which may also be a bromine source, and a carboxylic acid solvent selected from the group consisting of acetic, propionic, benzoic acids ranging between 0.05 to 0.3 wt. times with respect to toluene, at a temperature ranging between C. and pressures in the range of 1-10 bars for a period of 0.5-1.5 hours to obtain benzaldehyde (40-50%) along with other by-products.


  • Guest
Benzoic Acids to Benzaldehydes
« Reply #31 on: November 25, 2003, 03:16:00 PM »
Here is a moderately interesting preparation of a benzaldehyde from its corresponding benzoic acid, taken from  J. Org. Chem. 435-439 (1964). What I find hilarious with this synthetic sequence is the absurdly excessive amounts of solvents and reagents used - In the workup of 3,5-Dimethoxybenzyl Alcohol, a little over 20g of product is taken up in three liters of diethyl ether, and then washed with with two liters of water, and one liter each of  aqueous NaOH and brine! Then, to produce 12g of the corresponding benzaldehyde, five liters of hot chloroform is used in the reaction and workup... If someone was caught wasting so much chemicals these days, they would be fired on the spot

3,5-Dimethoxybenzyl Alcohol

3,5-Dimethoxybenzoic acid (25.0g, Rf 0.04) was dissolved in warm, dry tetrahydrofuran (400 mL), and this warm solution was added continuously over 90 min to a gently refluxing suspension of lithium aluminum hydride (10 g) in tetrahydrofuran (100 mL). When the addition was complete the mixture was boiled under gentle reflux for 4h, then cooled (ice-water bath). The excess hydride and the complex were decomposed by cautious addition of ethyl acetate (60 mL), water (60 mL), and 2N aqueous hydrochloric acid (100 mL) . The volume of the resulting suspension was reduced to 150 mL (rotatory evaporator, bath temperature of 40°C), diluted by addition of water (200 mL), and extracted with 6x500mL ether. The ether extract was washed with water (1 L), 2N aqueous sodium hydroxide (1 L), water (1 L), and brine (1 L), then dried over sodium sulfate. The solvent was eliminated from this dried extract, leaving a colorless solid (22.9g), which was crystallized from hexane, giving 3,5-dimethoxybenzyl alcohol as needles (21.8g, 94%), mp 46.5-47°C (lit.[7] mp 47-48°C); TLC Rf 0.14.[6]


Freshly prepared "active" manganese dioxide [8] (201g) was added to a solution of 3,5-dimethoxybenzyl alcohol (17.8g) in dry, ethanol-free chloroform (2 L), and the mixture was stirred in an atmosphere of nitrogen for 24 h at room temperature. The mixture was filtered, and the residue was washed with 6x500mL portions of boiling chloroform. The solvent was eliminated from the combined filtrate and washings, leaving a colorless crystalline solid (13.9g), mp 43-45°C. This was crystallized from pentane, giving 3,5-dimethoxybenzaldehyde as prisms (12.8g, 72%), mp 45-45.5°C (lit.[9] mp 48°C); TLC Rf 0.57.[6]

References & Notes

[6] Thin layer chromatography (TLC) was conducted using silica as the absorbant. 95:5 CHCl3/EtOAc as the developing solvent. and iodine as the visualizing agent; Rf values reported are only reproducible to ±0.05.
[7] J. Am. Chem. Soc. 70, 664 (1948)
[8] J. Chem. Soc., 1094 (1952)
[9] J. Am. Chem. Soc. 76, 133 (1954)


  • Guest
the best way to benzaldehyde
« Reply #32 on: November 25, 2003, 03:45:00 PM »
from toluene is in reality:
- oxidise the toluene to benzoic acid with KMnO4 or else
- or be bright and get some benzoic acid directly
- dehydrogenate the benzoic acid at 500°C in a furnace tube with ZnO as catalyst to benzaldehyde with 95percent selectivity in excellent yields (single pass).

This is a standard process in industry, but easily and safely adaptable for clandestine use. The advantage is the dehydrogenation being strongly endothermic and this way being inherently safe and the dehydrogenation is going to stop at the benzaldehyde as long the temperature doesnt exceed 550°C. Works for many substituted benz-dehydes also.

There are no further reagents or carrier gas needed. Some propane or better electricity for heating and done. Catalyst is good for some hundred hours before regeneration is needed - no problem.


  • Guest
Toluene to Benzaldehyde using Co(II)-Peroxygen
« Reply #33 on: November 25, 2003, 09:58:00 PM »
Oxidation of Substituted Toluenes to Benzaldehydes using Solid Peroxygen Sources Catalysed in the Presence of Bromide and Cobalt(II)Acetate
Craig W. Jones, Anthony Hackett, Ian Pattinson, Alexander Johnstone, Sharon L. Wilson

J. Chem. Research (Synopsis), 438-439 (1996)

J. Chem. Research (Miniprint), 2501-2525 (1996) Full Article

Substituted toluenes can be selectively oxidized to the aldehydes employing solid peroxygens in the presence of cobalt(II)acetate, acetic acid and an inorganic bromide source.


  • Guest
A question
« Reply #34 on: December 20, 2003, 06:37:00 PM »
- dehydrogenate the benzoic acid at 500°C in a furnace tube with ZnO as catalyst to benzaldehyde with 95percent selectivity in excellent yields (single pass).
There are no further reagents or carrier gas needed. Some propane or better electricity for heating and done.

This part confuses me, is there a mistake perhaps? In theory benzoic acid could be hydrogenated to benzaldehyde or benzyl alcohol could be dehydrogenated to benzaldehyde; but hydrogenation would require hydrogen gas and the catalyst sounds rather like a dehydrogenation than a hydrogenation catalyst. I'd appreciate a reference, the method sounds interesting you see.


  • Guest
Me too, please. ;-)
« Reply #35 on: December 21, 2003, 08:18:00 PM »
Also could you give whatever is on your mind regarding the basic apparatus setup Org?

Is something similar to an acetaldehyde apparatus? Does the ZnO have to be specially prepared?

Rh, in your reference, do you think that Oxone would bee a good solid peroxygen?

Also, do you think it would work for non-substituted toluene? (I guess that's why you posted it here but i better ask.)

'cobalt(II)acetate, acetic acid and an inorganic bromide source.'

Would these have to be omitted or left out in the case of non-substituted toluene?


  • Guest
Rh, in your reference, do you think that Oxone
« Reply #36 on: December 21, 2003, 10:44:00 PM »
Rh, in your reference, do you think that Oxone would bee a good solid peroxygen?

Also, do you think it would work for non-substituted toluene? (I guess that's why you posted it here but i better ask.)

'cobalt(II)acetate, acetic acid and an inorganic bromide source.'

Would these have to be omitted or left out in the case of non-substituted toluene?

1) Probably, but only if you cannot get any of the already tested oxidants - it will save you some ratio experimentation.

2) Yes.

3) No, it'll be the same.


  • Guest
« Reply #37 on: December 25, 2003, 08:10:00 PM »
moo, you are absolutely right, I confused some procedures, my bad....

Here is it right:
C6H5COOH + H2 = C6H5CHO + H2O
Hydrogen IS needed as reactand and carrier gas.

Appl. Catal. A. 220 (2001) 41-49

Catalyst preparation:
(As ZnO is the most active and selective catalyst here, which also works at lower temperatures I describe only the preparation of this)

Zinc basic carbonate - ZnCO3.2ZnO.3H2O - is heated under nitrogen (any inert gas will do the job I suppose) at a rate of 10°C/min up to 250°C and held at this temperature for 4hours. Then the temperature is rised (10°C/min) up to 400°C for 6min. then let cool down.

Reactor tube: Glass, 10-15mm length, 5mm diameter, filled with 0,5gram catalyst.
(Scale up by using the same catalyst/volume and length/width ratio)

Temperatur of the reactor:
325°C = 80% conversion by 100% selectivity - no byproducts.
360°C = 100% conversion with 95%+ selectivity - some toluene is formed.
Over 360°C the rate of produced toluene rises rapidly and some other byproducts form.

Oh, yes we talk here of deoxygenation of benzoic acid to benzaldehyde.  ;)
The water formed cools and makes temperatures controlable.

Bubble dry hydrogen through hot benzoic acid and attach a nozzle before the mix enters the hot tube - for security. (this is a MUST HAVE for all tube furnances! Its so easy to stay save)

Addon: If nitrogen is used as carrier gas and the hot tube flushed with nitrogen before use, at temperatures exceeding 400°C benzene is formed in good yields.

thanks moo for asking - now its fixed.  :)



  • Guest
Reference Uploaded
« Reply #38 on: December 30, 2003, 03:20:00 AM »
Applied Catalysis A: General 220 (2001) 41–49

Deoxygenation of benzoic acid on metal oxides
1. The selective pathway to benzaldehyde
M.W. de Lange, J.G. van Ommen, L. Lefferts



  • Guest
« Reply #39 on: December 30, 2003, 08:19:00 PM »
When you said Act. Mno4 needed to be used, for good yields, what do you consider good yields?  Once toulene is oxidize to benzaldeyde, what are the chances that the aldehyde will be oxid. futher after the temp rises.  To this day, I do not under Mn compounds, most of there mechanism or not completly understood. ADDkid 
Also, if the aldehyde is futher oxy. do you have to keep the temp cool for seprat.