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My A level exam board describes an experiment to produce methyl 2-hydroxybenzoate (methyl anthranilate) from methyl 2-aminobenzoate (methyl salicylate).

I did the experiment as described (including keeping the temperature below 5 degrees), but when I added the sodium nitrite solution, a significant amount of brown gas was produced, which I identified as nitrogen dioxide. My teacher said this shouldn't happen, and wasn't sure why it was happening. What is wrong with the plan?

Edit: I think too much sodium nitrite is used; calculation suggests about 3g of it should be added, so I think a decimal point is missing. Am I right in thinking this?

Here is the plan:

Requirements: 2-aminomethylbenzoate 5 cm3 (6.5 g), concentrated sulfuric acid 5.6 cm3 (10 g), sodium nitrate(III) solution 60 g in 100 cm3 water, urea (solid).
Measure out 45 cm3 of distilled water into a 250 cm3 conical flask. Slowly and carefully add 5.6 cm3 (10 g) of concentrated sulfuric acid to the water. Add to this warm solution 5 cm3 (6.5 g) of 2aminomethylbenzoate. (You may have to warm this first as its melting point is 24 ºC). Place the flask in an ice bath and add about 45 g of ice to the solution in the flask. Slowly add 20 cm3 of sodium nitrate(III) solution to the flask making sure that the temperature does not rise above 10 ºC. Now warm the solution slowly to 25 ºC and hold at this temperature for 5 minutes. Add about 4 g of solid urea to remove the excess sodium nitrate(III). Warm the solution to 80 ºC and then boil it for no more than 5 minutes. Pour the mixture into a 250 cm3 beaker that contains about 50 g of ice cubes. Separate the oily lower layer and dry using anhydrous sodium sulfate. Re-distill the oil. The boiling point of pure 2-hydroxymethylbenzoate is 223 ºC. Think about how you can check the identity of your product.

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  • $\begingroup$ Possibly. Also, you have to keep the reaction mixture cool (below about 5°C) otherwise the nitrous acid decomposes, producing nitrogen dioxide. $\endgroup$ – bon Feb 22 '16 at 19:03
  • $\begingroup$ Also, perhaps you could copy-paste the relevant experimental protocol into your question rather than posting a long, ugly link. $\endgroup$ – bon Feb 22 '16 at 19:24

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