Benzaldehyde

Legality: DEA Listed Chemicals

Production of this substance may be illegal in some jurisdictions under certain circumstances.

21CFR1310.02 a & b

In 1995/6, two lists were created "List I" and "List II", for which commercial manufacturers and distributors must register, and for which possession with the intent to manufacture illegal substances (such as methamphetamine, ecstasy, etc) is illegal. On these a few dozen "precursor" compounds commonly used in the manufacture of illegal drugs.

Bottom line: Do not produce this chemical without checking to make sure that you may do so legally.

 

 

Benzaldehyde
DEA LIST I/II SUBSTANCE

Chemical formula	C7H6O
OTP appearance	clear pale yellow liquid
Index of refraction	1.5456
Molar Mass(g/mol)	106.12
Density(g/cc)	1.044
Melting Point(°C)	-57.12
Boiling Point(°C)	178.1
Solubility in water(g/L)	7
NFPA 704	2 2 1

Uses

Benzaldehyde, like caffeine is an aromatic compound which occurs naturally. It provides an early and simple path to aromatics such as 4-aminobenzoic acid before the trimerization of acetylene is practical.

Other

• Feedstock for many aromatic chemicals
  • Benzene
  • Benzyl alcohol
  • Benzoic acid
  • Styrene

Natural occurrence

• Does occur naturally in bitter almonds and almond oil, apricot, peach, and cherry pits

Hazards

• GRAS

Production

Extraction

from amygdalin sources

The extraction of benzaldehyde and hydrogen cyanide from amigdalyn-bearing nuts is well known. This patent from 1922 describes a way of removing both from nut meats so that the resulting material is a safe foodstuff:

1. Blanch the whole nuts for 2 min in boiling water
2. Quench the blanched nuts in cool water
3. tumble the seeds lightly to removed skins
4. Dry in room temperature air
5. Slice, shave, or grind the nuts to increase permeability
6. Optionally, re-press to remove "fixed oil"
7. Immerse the cake in water between 27 and 40°C
8. HCN may be distilled from the water

The molecular weight of amygdalin is 457.429, that of benzaldehye is 106.12, so 23% of the mass of amygdalin will appear as benzaldehyde. Likewise 6% of the mass of amygdalin will appear as hydrogen cyanide.

Chemical yield

Source	Amigdalyn(%)	yield per kg of nutmeat		yield per tree/yr		yield per hectare/yr
		Benzaldehyde	Hydrogen cyanide	Benzaldehyde	Hydrogen cyanide	Benzaldehyde	Hydrogen cyanide
Cherry pit	3%	6.9g	1.8g
Peach Kernel	3%	6.9g	1.8g
Bitter almond	2%	4.6g	1.2g	115g (~1mol)	30g	9.2kg (~85mol)	2.4kg
Apricot kernel	2%	4.6g	1.2g
Prune kernel	1.5%	3.45g	0.9g

Synthesis

Etard reaction

1. Combine toluene with chromyl chloride in chilled dichloromethane
2. Add a chilled saturated solution of sodium sulfite
3. Wash/Extract benzoldehyde using DCM

retro aldol

Reflux cinnemaldehyde and sodium carbonate producing benzaldehyde and acetaldehyde

C₉H₈O + H₂O

{Na₂CO₃

→

8h}

C₇H₆O + CH₃CHO

oxidation of benzyl alcohol

via manganese dioxide

Combine benzyl alcohol with manganese dioxide

C₇H₈O + MnO₂

{CH₂Cl₂

→

}

C₇H₆O + H₂O + MnO

via persulfate

1. Prepare a saturated solution of ammonium persulfate
2. Prepare a mixture of benzyl alcohol with a small amount of water and methanol and stir strongly in a water bath
3. Add the persulfate solution dropwise to the alcohol solution.
   • Maintain strong stirring throughout the reaction
   • Keep bath temperature between 60 and 65°C
   • Keep the alcohol solution about 3°C higher than the bath

Purification

exposure to air

When exposed to air, benzaldehyde oxidises to benzoic acid:

2 C₆H₅CHO + O₂ → C₆H₅COOH

Prepare 1.5 volumes of saturated solution of sodium bicarbonate

1. Add 1 volume of benzaldehyde/benzoic acid solution, converting the acid to sodium benzoate

   C₆H₅COOH + Na₂CO₃ → C₆H₅COONa + CO₂ + H₂O

2. Allow to stand and separate
3. Retain the acetaldehyde layer

via adduct

1. Prepare a saturated aqueous solution of sodium bisulfite
2. Add benzaldehyde dropwise
3. Filter
4. Discard filtrate
5. Wash residue with dichloromethane
6. Prepare a saturated solution of sodium carbonate
7. Combine residue and solution with strong stirring
8. Allow to stand
9. Retain the benzaldehyde layer.