An organic conversion
Phthalimide
The next step was to convert the imide into anthranilic acid.
The more commonly used mechanism for this reaction is known as the Hofmann rearrangement; a cooled solution of sodium hydroxide is prepared, and in this process, bromine disproportionates when reacted with sodium hydroxide, into sodium bromide and sodium hypobromite. These hypobromite ions react with the imide, and the bromine substitutes for the hydrogen, which is bonded to the nitrogen, to give hydroxide ions. Then, the carbon bonded to this NBr group donates its bonding pair of electrons to the nitrogen atom, thus becoming positively charged, which can then be attacked by the lone pair on a hydroxide ion. Next, the N-Br bond undergoes heterolytic fission, wherein the Br takes both elections and is kicked off as a bromide ion; a nitrene is formed as an intermediate. From this nitrene, a lone pair of electrons on the nitrogen atom collapse onto to C-N bond to form a double bond, breaking the carbon’s bond to the benzene ring, and the electrons from that bond, dativ ely bond onto the nitrogen for a full outer shell. This forms an isocyanate, which adds on a water molecule in a nucleophilic addition step, while spontaneously losing carbon dioxide, to finally form the anthranilic acid.
Hofmann Rearrangement mechanism
The process used in NileRed’s method, however, is different. He first prepared a solution of sodium hydroxide, which was then cooled to 0°C in an ice bath. Then, bleach was added slowly, to keep the mixture below 5°C. Then, the imide was added, and with NaOH being a strong base, a hydrogen cation was ripped off the imide, neutralized with the hydroxide anion from the NaOH to form water and sodium phthalimide. From this point, a Hofmann rearrangement could occur in the presence of sodium hypochlorite, from the bleach, and sodium hydroxide, to convert the phthalimide into sodium anthranilate. To convert this anthranilate into anthranilic acid, he cooled the setup, and added hydrochloric acid. This was reacting with the sodium anthranilate in a displacement reaction to form sodium chloride and anthranilic acid. He continued to add the HCl to bring the pH down to 4; at this pH, the anthranilic acid is at its least water soluble, and so it was knocked out of the solution.
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