Benzaldehyde is a useful chemical in many pharmaceutical syntheses. A great it example is it's use to prepare mandelic acid, or cinnamic acid. It is also used as an artificial flavor, specifically almonds, or bitter almonds. It has a very sweet smell, not unlike nitroaromatics. Pure benzaldehyde is a clear, colorless liquid. It can be prepared by the sommelet reaction of benzyl chloride, or by the hydrolysis of benzal chloride.

Into a 1000ml flask, add 45g of hexamine. Prepare either a 60% ethanol solution by mixing 80ml of ethanol in 55ml of distilled water, or a 50% acetic acid solution by mixing 80ml glacial acetic acid with 80ml of distilled water. Swirl the flask at least enough to dissolve all visible solids - it doesn't have to become a completely clear solution, you just don't want a cake of hexamine at the bottom. Add 35ml of benzyl chloride to the flask and fit the reflux column to the flask. If you used ethanol, you can use a water bath, otherwise, use an oil bath to heat it to reflux and hold it there for about two hours. Prepare a ~10% solution of hydrochloric acid by mixing 20ml of 31.45% with 40ml of distilled water, or 30ml of 20% with 30ml of distilled water. After the materials in the flask have refluxed for two hours, add the above solution of hydrochloric acid to it and continue refluxing for at least 15-20min. After this, remove the flask from the bath and let it cool to room temp. You should see two layers, the bottom layer is usually a light orange and the top layer can be yellow to orange. The top layer is your benzaldehyde.

Set the flask up for simple distillation and begin heating it on an oil bath.  You will now be steam distilling the benzaldehyde from the reaction mixture/by products.  After many tests, I have found this to be the most efficient (and easiest method) to obtain the benzaldehyde.  If you used ethanol, collect the first fraction all the way up to ~98C.  Now, collect everything else distilling over (whether you used ethanol or acetic acid) until the distillate is runnnig out is mostly clear and benzaldehyde free.  You may need to add more water to the distilation flask to aid in the steam distillation.  

If you used ethanol, take the first fraction you collected and add it to a 500ml separatory funnel.  Dilute it with about the same volumn of distilled water and shake.  Let the layers separate and drain the bottom (aqueous) layer.  Add the rest of the distillate you collected (with a very obvious difference in layers) and dilute with enough water to fill the funnel up.  Drain off the lower (aqueous) layer, saving the benzaldehyde.  If you used ethanol, wash the benzaldehyde a few times with plain distilled water.  Be conservative on the water you use though, because benzaldehye is a little soluble in pure water.  If you used acetic acid, you must neutralize the benzaldehyde by washing it a few times with dilute sodium (bi)carbonate solution and distilled water.  Clearly, it is much more beneficial to use the ethanol solution as opposed to the acetic acid solution.  Once the benzaldehyde has been washed/neutralized, dry it with magnesium sulfate. It should be a clear yellow to clear orange liquid now. Distill the benzaldehyde under reduced pressure to minimize decomposition. Use a nomograph to predict the boiling point of the pure benzaldehyde. You can also distill it under atmospheric pressure, but expect slight decomposition. Collect the portion coming over between 178-180C. Theoretical yeild is 29.4g. Last time I attempted this, I obtained ~22g which is about a 75% yeild; 70% yeilds are standard for this procedure.

When distilling, it would behave badly.  There actually is a significant portion of BnCl in the toluene that is distilled off, this is why I suggest re-using it repeatedly.  Right after toluene's boiling point, it continues to make a steady rise all the way up to BnCl's boiling point, distilling the whole way up.  So while maybe the fraction at 115C is 1%BnCl and 99% toluene, it changes with the curve.  This is exactly what would happen if you had a mixture of benzaldehyde and toluene. 

However, you could ppt the benzaldehyde as the bisulfite adduct, where as the toluene could simply be separated off, but the more you dick around with a substance, the more you lose.  So to answer your question, yes, you could technically use the entire filtered mixture from BnCl preparation to produce benzaldehyde, but expect much loss of yeild haha.

For the record, BnCl = benzyl chloride

C6H5CH2OH + 2HNO3 ----> C6H5CHO + 2H2O + 2NO2

When doing oxidations with nitric acid, the byproducts always include nitrogen dioxide and water.  That would certainly be nice if you could oxidize 2.5 moles of a substance with 1 mole of HNO3, wouldn't it

As for the oxidation, I don't know if it will work with HNO3 so don't get your hopes up.  When I used HNO3 to oxidize organics, it usually took them all the way to their carboxylic acid (sucrose to oxalic acid, lactose to mucic acid). 

That has a much better chance of working.  I've seen potassium dichromate used to create aldehydes many times.  Acetaldehyde, anisaldehyde (from anethole), etc.  I would suggest experimenting.

Personaly, even with the dangers associated with it, if I had Potassium Dichromate I would synthesis Chromyl chloride and use that to oxidise Toluene in high yeilds via Etard reaction. ...

Now, this particular bee has just ordered 200g of potassium dichromate. It is good to read that it has other uses. However, "playing" with chromyl chloride might be a bit too hardcore for this particular citizen chemist, so it won't be attempted.
How ever, electrochemical preparation of benzaldehyde will be explored, as 500g of both labgrade ammonium sulphate and manganese sulphate has been ordered for this very purpose.

Well this bee DOES indeed have a tyvek suit and a gas mask, too bad that the mask is a 20year old military surplus one.  

CrO2Cl2 reacts with water to release hydrochloric acid (HCl) and hexavalent chromium (CrVI)

Acute: HCl can be acutely lethal. Exposure to chromyl chloride vapour irritates the respiratory system and severely irritates the eyes, and the liquid burns the skin and eyes. Ingestion would cause severe internal damage.[4]

Chronic: CrVI can produce chromosomal aberrations and is a human carcinogen via inhalation.[5] Frequent exposure of the skin to chromyl chloride may result in ulceration.[4]

Thus, CrO2Cl2 should be carefully handled in a well ventilated area. CrO2Cl2 is so aggressive that its storage can be problematic as it attacks rubber and most plastics as well as greases.

Hexavalent chromium chromium does not sound too healthy, and it is also hard to dispose it properly (ie not flushing it down the toilet).

How ever, googling uncovered a video on the synthesis of chromyl chloride:
 http://www.youtube.com/watch?v=D9qEmaiYSPk

The guy apparently does it in a fume hood.

Also consider BnOH + HCl = BnCl
Then you just need to react with hexamine and get benzaldehyde.

check these out.....88% yield.  I got these when i googled how to make clayfen and found Rhodium link with info and references that I followed and found the following of interest..

The oxidation of benzyl alcohol is representative of the general procedure employed. MnO2 'doped' silica

made by - 0.348 g of manganese dioxide and 0.652 g of silica were ground in a pestle-mortar to prepare 35% MnO2-Silica. This then being 
(1.25 g, 5 mmol of MnO2 on silica gel, Scientific, 230-400 mesh with large surface area of 600m2/g) is thoroughly mixed with benzyl alcohol (108 mg, 1 mmol) and the material
is placed in an alumina bath inside the MW oven and irradiated for 20 seconds. Upon completion of the reaction, monitored on TLC (hexane:AcOEt, 10:1), the product is extracted into methylene chloride, solvent removed and the residue passed through a bed of silica gel (4 cm) to afford exclusively benzaldehyde. The overoxidation to carboxylic acid is not observed. The same reaction could be completed in 2 h at a comparable temperature of 55 °C in an oil bath


and this, if you want to play around with Clayfen..around 92%

We report here a facile oxidation of alcohols to carbonyl compounds using montmorillonite
K10 clay-supported iron(III) nitrate, clayfen, 6,7 under solvent-free conditions in a process that is accelerated by microwave irradiation. The reaction presumably proceeds v/a the
 intermediacy of nitrosonlum ions, 6b and no formation of carboxylic acids occurs. The experimenta
l procedure involves a simple mixing of neat alcohols with clayfen and irradiating the reaction mixtures
 in a microwave oven for 15-60 seconds in the absence of any solvent.

The limitation with aliphatic alcohols, however, still persists and the protocol gives a mixture of compounds.   

Might be of interest to see what they would be anyways..

I am pretty sure an aluminum bath is made say from aluminum hydroxyd  blasted to an oxide, which is OTC

I am blown away by this basically,, I am seeing things in the literature where dry reagants are literally placed in a mortar, ground, perhaps heated, reground, then extracted to find great yields.

I hope these are of interest to you all..I know they are to me.. apologies big time if this has already been thrashed incessantly.. I don't check all the boards what not..

2b

ps I attached a clayfen and claycop prep for those who may find this good, and via the said articles and not Rhodiums take on this..

I've checked a little on the commercial equipment, and as expected it's astronomically expensive.

PP

For no reason.  Microwave chemistry can be accomplished with the same pieces you use for standard reactions.  A flask that fits in the microwave, and a reflux column.  Whatever reflux column you use should be used every time (so be prepared to commit haha).  Cut a hole through the top of the microwave, just big enough so the column barely fits through.  Remember, you'll want the water jacket, or at least the water outlet, outside of the microwave.  This will serve suitable for many reactions.

Prepuce,, google search this for a good description.

"Solvent-free organic synthesis - Google Books Result"

or better still check this site out, and download the book for free..


http://scientist-at-work.blogspot.com/      and scroll a fair bit down and youll see it.. It has some GOOD(insert understatement here) books, I got the clayden solutions manual to one of the best modern org chem books.. plus a shitload of others....

So with this solventless chem, and doing this in an unmodified microwave, one would surely have to be FUCKING CAREFUL, and really understand what is happening. I am not an expert and currently exploring this, and sharing along the way. Alumina I belive is the oxide of aluminium and can easily be got or made.


2b

ps , and excerpt from that book

In a typical experiment, benzaldehyde (106 mg, 1 mmol) was added to the finely
powdered paraformaldehyde (60 mg, 2 mmol). To this mixture, powdered barium
hydroxide octahydrate (631 mg, 2 mmol) was added in a glass test tube and the
reaction mixture was placed in an alumina bath (neutral alumina: 125 g, mesh
_150, Aldrich; bath: 5.7 cm diameter) inside a household microwave oven and
irradiated for the specified time at its full power of 900 W intermittently or
heated in an oil bath at 100–110_C. On completion of the reaction, as indicated
by TLC (hexane-EtOAc, 4:1, v/v), the reaction mixture was neutralized with dilute
HCl and the product extracted into ethyl acetate. The combined organic extracts
were dried over anhydrous sodium sulfate and the solvent removed under
reduced pressure. The pure benzyl alcohol (99 mg, 91%), however, is obtained
by extracting the reaction mixture with ethyl acetate prior to neutralization and
subsequent removal of the solvent under reduced pressure.

References: R.S. Varma, K.P. Naicker, P.J. Liesen, Tetrahedron Lett., 39, 8437 (1998).