Sciencemadness Discussion Board » Fundamentals » Beginnings » 4-Methylbenzaldehyde... Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues

Author: Subject: 4-Methylbenzaldehyde...
Alkyrisk
Harmless

Posts: 6
Registered: 15-11-2009
Location: Transilvania
Member Is Offline

Mood: No Mood

4-Methylbenzaldehyde...

Hello chemistry fans. Im uninitiated in mysteries of chemistry but i want to start a pretty hard experiment and i dont have all substances that i need. The first one is 4-Methylbenzaldehyde. I know only one method to obtain this substance by Friedel-Crafts formylation of toluene under Gattermann-Koch conditions. If someone else has tried and succeeded in another way he will be very helful for me. Pyrrole and propionic acid are other substances that i need but i think it may be possible to buy them from somewhere. Here is the process that i know but i cant realize:

Nicodem
Super Moderator

Posts: 4230
Registered: 28-12-2004
Member Is Offline

Mood: No Mood

It is not at all easy to obtain 4-methylbenzaldehyde by toluene formylation, because all the amateur friendly methods fail on such poorly nucleophilic substrates. So you are left by either oxidation of p-xylene or varius multistep routes from toluene.

The oxidation of p-xylene can be performed with CrO3 in acetic anhydride. There might be other reagents as well but none particularly readily available. Oxone would be the most OTC, but the oxidation is a free radical chain mechanism based process and thus non-upscalable and prone to go out of control. With some care and thought it might be useful nevertheless. See also the methods discussed here and here (most are applicable to xylenes as well). You could use the cheap xylene mixture of regiosomers and then somehow separate out the 4-methylbenzaldehyde (fractionation and/or recrystallization of the bisulfite adduct, etc.).

Two step methods starting from toluene would be either chloro- or bromomethylation followed by either Kornblum oxidation or the Sommelet reaction. The problem is in that chloromethylation gives essentially a 1:1 mixture of para- and ortho-methylbenzyl chloride and a fume hood is needed because during the reaction small amounts of the carcinogenic bis(chloromethyl) ether form. This is no problem if you are careful, but beginners are usually not careful. Bromomethylation would be more selective for the para-methylbenzyl bromide, so it would be a better option but you need HBr. Partial separation might be possible via fractionation during the vacuum distillation if you have an efficient distillation column. Further separation of regioisomers could be achieved during the distillation of the benzaldehyde products. The para-methylbenzyl halides can also be prepared via radical halogenation of para-xylene (or xylenes mixture followed separation). This can be done by heating of NBS in a large excess of xylene in the presence of benzoyl peroxide or on sunlight. Alternatively trichloroisocyanuric acid can be used instead NBS to give the chloride. Elemental chlorine with a strong source of light or sunlight can also be used (see here).
The other possibility is to electrophilicaly iodinate toluene (which can be done highly selectively toward the para-iodotoluene), then make a Grignard reagent and react it with dimethylformamide (this is done in one-pot). An ultrasound bath would come handy here to start the magnesium insertion.

A two step protocol for formylation with chloral hydrate might be aplicable to toluene. I'm not sure if toluene is still within the reaction scope (if it is it must be on the edge), but essentially you alkylate an aromatic substrate with chloral in the presence of an acid to give Ar-CH(OH)CCl3 which when treated with a base releases the benzaldehyde. Check if it works on toluene here, here and the references there.

…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)

Alkyrisk
Harmless

Posts: 6
Registered: 15-11-2009
Location: Transilvania
Member Is Offline

Mood: No Mood

Firstly, thanks a lot for quickly answer (14.10 - 15.10 exactly one hour) it was just what I needed because tomorrow at school i must start working at this experiment, oh i forgot to say. I want to obtain finally, meso-tetraphenylporphyrin. Now i will read again your post (including "heres") and tomorrow i hope i can succeed in one of them and then to thank you glorious.
Ozonelabs
Hazard to Others

Posts: 120
Registered: 5-4-2008
Member Is Offline

Mood: Oligomerised

meso-tetratolylporphyrin no?

Otherwise for the meso-tetraphenylporphyrin you'd only need benzaldehyde as opposed to the 4-methyl derivative.

Alkyrisk
Harmless

Posts: 6
Registered: 15-11-2009
Location: Transilvania
Member Is Offline

Mood: No Mood

meso-tetratolylporphyrin??? YES that`s it. My mistake I copied and pasted the wrong name from wikipedia. Thanks for your vigilance.

 Sciencemadness Discussion Board » Fundamentals » Beginnings » 4-Methylbenzaldehyde... Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues