Camphor structural elucidation

Camphor structural elucidation

• 1.
  Dr. A. SyedMohamed Senior Assistant Professor and the Head Research Dept. of Chemistry Sadakathullah Appa College, Tirunelveli, Tamilnadu, India E-mail : [email protected] Structural Elucidation of Camphor CH3 O CH3CH3
• 2.
  It is amain constituent of camphor oil obtained from the wood and leaves of the camphor tree (Cinnamomum camphora) Camphor
• 3.
  Structure of Camphor 1.Molecular formula C10H16O 2. Saturated characteristics No addition with bromine, forms only monosubstitution products like mono-bromocamphor etc. Therefore, Camphor is a saturated compound and does not contain any double bond Facts: (i) it does not react with 1% alk. KMnO4 and (ii) molecular refraction also favours this. 3. Presence of a keto group Forms an oxime with hydroxylamine, semicarbazone with semicarbazide, phenylhydrazone with phenylhydrazine.
• 4.
  Camphor on oxidationwith nitric acid, yields a dicarboxylic acid called camphoric acid without loss of carbon atoms. On reduction with sodium amalgam, yields a secondary alcohol called borneol. Hence, camphor must be a cyclic ketone. When camphor is distilled with iodine, it yields carvacrol.
• 5.
  4. Bicyclic system Molecularformula of saturated parent hydrocarbon of camphor is C10H18 (Cn H2n-2 of bicyclic compounds) and, therefore, camphor is a bicyclic compound. 5. Presence of -CH2CO group On treatment with amyl nitrite and hydrochloric acid, it yields an iso- nitroso (oximino) camphor in which two hydrogen atoms have been replaced by = NOH group. This reaction reveals that the >C=O group is directly attached to a -CH2 group.
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  6. Presence ofa six-membered ring Formation of p-cymene reveals the presence of i. six-membered ring, ii. methyl and iii. gem-dimethyl groups.
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  7. Nature ofthe carbon-frame in camphor Camphor Camphoric acid Camphoronic acid C10H16O C10H16O4 C9H14O6 Camphor on oxidation with nitric acid, it yields a crystalline dibasic acid, camphoric acid, C10H16O4. As camphoric acid possesses the same number of carbon atoms as camphor, it means that the keto group must be present in one of the rings in camphor. Thus, during the conversion of camphor into camphoric acid, the opening of ring containing the keto group occurs and therefore, camphoric acid must be a monocyclic compound. A A O A OH O
• 8.
  When camphoric acidis further oxidised with nitric acid, camphoronic acid is obtained. In order to elucidate the structure of camphor, the structure of camphoric acid and camphoronic acid should be known. Structure of camphoronic acid 1. Molecular formula C9H14O6 2. Saturated tricarboxylic acid - C6H11 (COOH)3 and its parent hydrocarbon will be C6H14 (CnH2n+2) for acyclic compound, indicating that camphoronic acid is an acyclic compound. 3. Camphoronic acid does not undergo decarboxylation, three - COOH groups should be attached to three different carbon atoms.
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  In order toexplain the formation of these products, Bredt suggested that camphoronic acid is a, a, b - tricarballylic acid (I).
• 10.
  Synthesis of camphoronicacid
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  Structure of camphoricacid 1. Molecular formula C10H16O4. 2. By usual tests, it is a saturated dicarboxylic acid. 3. Camphoric acid should be monocyclic. 4. As camphoric acid is able to form a monoester readily but it forms diester with difficulty, this shows that the two carboxyl groups are not similar, i.e., one is primary or secondary and the other it tertiary. Facts Camphoric anhydride forms only one monobromo derivative with phosphorus / bromine. Hence, one of the carboxyl groups is secondary, ie. the carbon atom of one carboxyl groups must be 1C.
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  5. Structure ofcamphoric acid may be given as follows
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  Synthesis of Camphoricacid
• 14.
  Structure of Camphor Onthe basis of the foregoing discussion the structure of camphor may be given as either III or IV. Camphor gives carvacrol on distillation with iodine. This is possible only from structure III and not form structure IV.
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  Synthesis of Camphor
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  Stereochemistry of Camphor Camphorhas two dissimilar chiral centres but only one pair of enantiomers is known. This is due to the fact that only the cis- form is possible; trans fusion of the gem-dimethylmethylene bridge to the cyclohexane ring is impossible. Thus only the enantiomers of the cis-isomer are known. Camphor and its derivatives exist in the boat conformation. Since the gem-dimethyl bridge must be cis, the cyclohexane ring must have the boat form.