An unknown sample was given to Wendy. As per the procedure, she diluted her unkn
ID: 514212 • Letter: A
Question
An unknown sample was given to Wendy.
As per the procedure, she diluted her unknown pale yellow sample in a mixture of water and dioxane. She then added 6M sodium hydroxide and iodine test solution in small portions. The solution turned a yellow color after pouring into water without the formation of a precipitate.
She took another sample of the her unknown and added it dropwise to a mixture of semicarbazide HCl, sodium acetate and water. After heating and recrystallization she obtained and orange yellow solid with a melting point of 212-215ºC.
She took 5 drops of her unknown and diluted in 5 mL of ethanol. This pale yellow solution was added to 2,4-dinitrophenylhydrazine. The red orange product formed was vacuum filtered and determined to have a melting point of 252-254ºC which is very close to the boiling point (251-252ºC) of the unknown.
She ran an IR and labeled the following peaks as significant.
3083 cm-1
2814 cm-1
2743 cm-1
1678 cm-1
1627 cm-1
1124 cm-1
Out of the options shown, what unknown was given to Katrina?
Hint: The following table might prove useful
) acetophenone
) cinnamaldehyde
) heptanal
) benzaldehyde
) furfural
) acetone
) cyclopentanone
) cyclohexanone
) hexanal
) 3-hexanone
) propiophenone
) 2-butanone
) piperonal
) pivaldehyde
) phenylacetaldehyde
) salicylaldehyde
) 2-tolualdehyde
) 3-tolualdehyde
) 2-hexanone
) 1-naphthaldehyde
) pentanal
) 3-pentanone
) butanal
) veratraldehyde
) 4-tolualdehyde
) 2-pentanone
Table of Aldehyde & Ketone Derivatives mp C tests. Compound bpoc DNPH Semi C Oxime Idfm. Bndct 1. Naphthaldehyde 292 oil 221 98 2, 2-Hexanone. 128 oil 121 144 yes 3. 3 Hexanone 125 oil 113 130 no RO 4, Pivaldehyde 85 oil 134 oil 5. Hexanal 131 104 106 51 yes 6. Pentanal 103 107 oil 52 yes 7. Heptanal 155 108 109 8. Phenylacetaldehyde 194 110 97 9. 2-Butanone 115 135 yes 01 10. Butanal. 75 123 96 oil RO 11. Acetone. 56 126 190 59 yes no 12. 2 Pentanone. 102 143 112 oil yes 13. cyclopentanone 146 131 210 56 no no 14.. 3-Pentanone 102 156 138 oil no 15 cyclohexanone 156 162 166 91 16 Propiophenone. 190 173 54 no no 17. 2-Tolualdehyde. 200 193 209 49 no 18 3-Toualdehyde 199 212 204 60 19, Furfural 161 212 75 202 no no 20 4 Tolualdehyde 204 232 234 80 21. Benzaldehyde 179 237 240 22 Acetophenone 205 203 60 yes n0 23. Salicylaldehyde 197 248 231 no 24. Cinnamaldehyde 252 255 64 no 25, Veratraldehyde 285 261 94 no 26. Piperonal 263 265 146 230 Note: DNPH s dinitrophenylhydrazone Semic semicarbazone ldfm z iodoform test Bndct Benedict's testExplanation / Answer
1. Since precipitate is not formed in Iodoform test, the unknown compound is not a ketone. So, ketones in the list are eliminated.
2. Since yellow solide is formed in Semicarbazone test, the unknown compound is an aldehyde and the melting point of 212-215ºC indicates the presence of Cinnamaldehyde (Refet table of aldehyde and ketone derivatives).
3. The Dinitrophenyl hydrazone test obtained a melting point of 252-254ºC which is close to 255ºC of Cinnamaldehyde. It is given that the boiling point of the unknown is 251-252ºC and boiling point of Cinnamaldehyde is 252ºC. These 2 factors confirm the presence of Cinnamaldehyde.
4. IR spectrum: Presence of 2814 cm-1 indicates the presence of -C-H aldehydic (2900-2800 cm-1), Presence of 3083 cm-1 indicates the presence of =C-H stretch. This again confirmed the presence of Cinnamaldehyde.
So, the unknown is Cinnamaldehyde.
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