Take few drops of onion juice, dilute vanilla essence and clove oil in three different test tubes and consider the following statements: 1. The characteristic smell of onion vanishes upon addition of NaOH, however it persists with HCl 2. The characteristic smell of vanilla is lost upon addition of HCI, however it persists with NaOH. 3. The characteristic smell of clove oil is lost upon addition of NaOH in it. How many of the statements given above are correct

Effect of NaOH

• The characteristic smell of onions is primarily due to sulphur compounds, such as allyl sulphides and thiosulfates, which are released when the onion is cut or crushed. These compounds are responsible for pungent odour
• Effect of Sodium Hydroxide (NaOH): NaOH is a strong base that can react with sulphur-containing compounds. When NaOH is added to onion juice, it can neutralize some of the acidic components and interact with the sulphur compounds, leading to a reduction or change in the odour. It does not change its smell with acid. Hence, statement 1 is correct.
• It can cause the saponification of vanillin to some extent, potentially leading to the formation of vanillinates.
• This reaction may alter the aroma of vanilla, potentially reducing its intensity or changing its characteristic scent.
• Eugenol (4-allyl-2-methoxyphenol) is the compound responsible for the characteristic smell of cloves. It is a phenolic compound with a hydroxyl group (-OH) attached to an aromatic ring. It can react with phenolic compounds like eugenol. The reaction can convert eugenol into its sodium salt form, known as eugenolate.
• This reaction changes the structure of eugenol, affecting its aromatic properties.
• Effect on Smell: The conversion of eugenol to eugenolate results in a change in the chemical structure of the compound. The sodium salt form is less volatile and less likely to evaporate, which can lead to a reduction in the intensity of the clove smell. Hence, statement 3 is correct.
• Reduced Aroma: Because eugenol is less volatile in its salt form, the overall smell of the clove oil might diminish or become less pronounced after the addition of NaOH.

Effect of HCl

• HCl, being a strong acid, may react with vanillin but typically does not cause significant changes unless the concentration is very high or prolonged exposure occurs. Hence, statement 2 is incorrect.
• In practice, under normal conditions, HCl is less likely to significantly alter the smell of vanilla compared to NaOH.