Addition of Bisulfite to Aldehydes

• Benzaldehyde 
• Sodium bisulfite

Apparatus and glass wares:

• 3 graduated cylinder with stopper 500 mL
• beaker 200 mL
• Erlenmeyer flask with stopper 250 mL
• temperature probe
• temperature measuring device

Experimental procedure:

Using an Erlenmeyer flask with stopper, 108 g of sodium bisulfite are dissolved in 200 mL of dist. water. Sodium bisulfite dissolves in water to form bisulfite ions. The solution of bisulfite is poured into a graduated cylinder containing 116 mL of benzaldehyde. The stoppered cylinder is shaken vigorously. After removing the stopper a temperature probe connected to a temperature measuring device is inserted into the reaction mixture.

Results:

With an exothermic reaction the content of the graduated cylinder solidifies.

Discussion:

The characteristic reaction of aldehydes and ketones is addition across the carbon-oxygen double bond. Because of polarization of the C=O bond, the carbon atom of the carbonyl group becomes electron-deficient, acquiring a partial positive charge. This makes it susceptible to nucleophilic attack by an electron-rich chemical species. In the present case, bisulfite ion is added to the electrophilic center. Since the sulfur atom of bisulfite has an unshared pair of electrons it can act as a nucleophile and form a bond to carbonyl carbon⁽¹⁾

In general, aldehydes are more reactive than ketones. There is a combination of steric hindrance and inductive effects that makes ketones to react slower than aldehydes ⁽²⁾.

steric hindrance carbonyl carbon

• Bulky alkyl groups sterically hinder the approach of nucleophile.
• The electronic effects of alkyl substituents are weakly electron donating. So they make the C atom in carbonyl less electrophilic

The addition of bisulfite is usually employed to purify aldehydes. Aldehydes are isolated from reaction mixtures through its bisulfite derivatives. The addition compound can be split easily to regenerate the aldehyde by treating it with either dilute mineral acid or dilute alkali.

Original doc

Benzaldehyde

Packaging & Delivery

Packaging Detail: 200kg/drum or as required

Specifications

• CAS#: 100-52-7
• EINECS# 202-860-4
• MF: C7H6O
• MW: 106.12
• Purity: 99.0%
• mp -26 °C
• bp 179 °C
• density 1.05
• vapor density 3.7 (vs air)
• vapor pressure 4 mm Hg ( 45 °C)
• Appearance: Colourless liquid

Application:

Application: Benzene formaldehyde is medicine, dyestuff, spices and resin industry an important raw material, but also can be used as a solvent, plasticizer and low temperature lubricant, etc. In essence industry is mainly used to allocate flavouring essence, a few used for cosmetic essence and cigarette flavor.