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Org. Synth. 1946, 26, 97
DOI: 10.15227/orgsyn.026.0097
o-TOLUALDEHYDE
Submitted by Jonathan W. Williams, Charles H. Witten, and John A. Krynitsky.
Checked by W. E. Bachmann and N. C. Deno.
1. Procedure
Thirty grams (0.14 mole) of o-toluanilide (Note 1) and 20 ml. of dry benzene are placed in a 125-ml. Claisen flask which is fitted with a condenser for distillation under reduced pressure and set in a water bath. The bath is heated to 50°, and 30 g. (0.14 mole) of phosphorus pentachloride is added to the mixture over a period of 10 minutes. The bath is then heated to 75°, and this temperature is maintained for 15 minutes. The benzene and most of the phosphorus oxytrichloride are then removed by distillation at 20 mm. from a bath at 95°. The crude N-phenyl-o-toluimidyl chloride which remains as a viscous liquid is sufficiently pure for the next step.
A mixture of 50 g. (0.26 mole) of anhydrous stannous chloride (p. 627) and 225 ml. of dry ether is placed in a 1-l. three-necked round-bottomed flask fitted with a rubber-tube sealed stirrer, an inlet tube reaching nearly to the bottom of the flask, and a reflux condenser (Note 2) protected by a calcium chloride drying tube. The mixture is saturated with dry hydrogen chloride (Note 3) with continuous stirring. Within 3 hours all the stannous chloride dissolves, forming a clear viscous lower layer. The source of hydrogen chloride is then disconnected, and the freshly prepared imidyl chloride is transferred into the mixture with the aid of 25 ml. of dry ether (Note 4). Stirring is continued for 1 hour, and then the reactants are allowed to stand at room temperature for 12 hours.
Ice (about 100 g.) and then 100 ml. of cold water are added, the mixture is stirred for 10 minutes, and then the ether is removed by distillation (Note 5). To the residue in the flask is added sufficient water to make the total volume about 300 ml. Steam distillation is then carried out until the distillate comes over clear. This process requires about 1 hour. The aldehyde is extracted from the steam distillate with three equal portions of the ether recovered above, and the ether solution is dried for several hours over anhydrous sodium sulfate.
The ether is removed by dropping the solution slowly from a separatory funnel into a 50-ml. Claisen flask fitted with a condenser for downward distillation and heated on a steam bath (Note 6), and the residual aldehyde is distilled under reduced pressure. The yield of o-tolualdehyde boiling at 90–93°/19 mm. is 10.5–12 g. (62–70%).
2. Notes
1. The o-toluanilide was prepared by the reaction of o-tolylmagnesium bromide with phenyl isocyanate.1 If the o-toluanilide has been recrystallized from petroleum ether, it may be necessary to melt the light fluffy crystals (to a more compact form) in order to get all the compound into the flask.
2. A reflux condenser is not necessary if the mixture is kept ice-cold during the addition of hydrogen chloride.
3. The checkers used hydrogen chloride from one of the cylinders of hydrogen chloride now available commercially.
4. At this point considerable evolution of heat occurs. A cold-water bath should be kept in readiness for application to the reaction flask.
5. The distillate, which may contain a small amount of o-tolualdehyde, is collected and used for the subsequent extraction.
6. In this step the recovered ether is collected in a dry atmosphere, and about 100 ml. of this ether is used in two portions to extract the sodium sulfate residue in order to transfer into the flask any small quantities of the aldehyde that may have been trapped by the drying agent.
3. Discussion
o-Tolualdehyde has been prepared by the oxidation of o-xylene,2 3 4 by the oxidation of o-xylyl chloride,5 by the oxidation of o-tolylcarbinol,6 by the reaction of o-tolylmagnesium bromide with ethyl formate,7 ethyl orthoformate,8,9 ethoxymethyleneaniline,9,10 N-methylformanilide,8 or with carbon disulfide followed by treatment with semicarbazide,9 and by the aluminum amalgam reduction of N,N'-diphenyl-N-carbethoxy-o-toluamidine.11 The procedure described is based on the method of Sonn and Müller,12 as studied for o-tolualdehyde by King, L'Ecuyer, and Openshaw.13
An excellent preparative method from α-bromo-o-xylene has been published.14
This preparation is referenced from:

References and Notes
  1. Schwartz and Johnson, J. Am. Chem. Soc., 53, 1066 (1931).
  2. Fournier, Compt. rend., 133, 635 (1901);
  3. Law and Perkin, J. Chem. Soc., 91, 263 (1907);
  4. Bornemann, Ber., 17, 1467 (1884).
  5. Rayman, Bull. soc. chim. France, (2) 27, 498 (1877).
  6. Fournier, Compt. rend., 137, 717 (1903).
  7. Gattermann and Maffezzoli, Ber., 36, 4152 (1903).
  8. Smith and Bayliss, J. Org. Chem., 6, 437 (1941).
  9. Smith and Nichols, J. Org. Chem., 6, 489 (1941).
  10. Monier-Williams, J. Chem. Soc., 89, 273 (1906).
  11. Shirsat and Shah, J. Indian Chem. Soc., 27, 13 (1950).
  12. Sonn and Müller, Ber., 52, 1929 (1919).
  13. King, L'Ecuyer, and Openshaw, J. Chem. Soc., 1936, 352.
  14. Org. Syntheses, 30, 99 (1950).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

petroleum ether

phosphorus oxytrichloride

N-phenyl-o-toluimidyl chloride

imidyl chloride

hydrogen chloride (7647-01-0)

Benzene (71-43-2)

ether (60-29-7)

phosphorus pentachloride (10026-13-8)

sodium sulfate (7757-82-6)

stannous chloride

aluminum (7429-90-5)

carbon disulfide (75-15-0)

Ethyl orthoformate

ethyl formate (109-94-4)

semicarbazide (57-56-7)

phenyl isocyanate (103-71-9)

ethoxymethyleneaniline (6780-49-0)

N-methylformanilide (93-61-8)

o-Xylene (95-47-6)

o-Tolualdehyde (529-20-4)

o-toluanilide

o-tolylmagnesium bromide

o-xylyl chloride (608-23-1)

o-tolylcarbinol (89-95-2)

N,N'-diphenyl-N-carbethoxy-o-toluamidine

α-bromo-o-xylene (89-92-9)