Volatile Oils: Esters, Aldehydes, and Ketones PDF

# Esters - Many of the volatile oils own their odor or their flavoring & perfume to esters, e.g. acetates of terpineol, borneol & geraniol. - Aging of Perfume: Storage of volatile oils permit esterification to take place, thus improve their smell & value. ## Isolation of esters 1. Few esters solidi...

# Esters - Many of the volatile oils own their odor or their flavoring & perfume to esters, e.g. acetates of terpineol, borneol & geraniol. - Aging of Perfume: Storage of volatile oils permit esterification to take place, thus improve their smell & value. ## Isolation of esters 1. Few esters solidify at room temp. and thus be readily separated from the oil by cooling, ex: benzyl benzoate. 2. Esters as methyl anthranilate can be isolated from essential oils by shaking the oil with dil. H2SO4, & purified by recrystallization with alcohol 3. Fraction distillation under vacuum: Oil must be free from organic acid before distillation to prevent the hydrolysis of the ester during distillation ## Identification of esters: By Saponification. R.COOR' + NaOH → RCO`ONa + R'OH : The ester can be identified by identifying the corresponding acid and alcohol, separately. ## Important Esters Occurring in Volatile Oils: 1. Esters of Aliphatic acid: Geranyl acetate & linalyl acetate. 2. Esters of Aromatic acids: benzyl benzoate & methyl salicylate. 3. Esters containing nitrogen (Amine esters): methyl anthranilate. ### Table 1: Important Esters Occurring in Volatile Oils | Vol oil | Structure | 1- Ester of aliphatic acids | |:---|:---|:---| |Geranyl acetate | | Oil of citronella, lemongrass, petit grain, lavender, coriander,.. Fraction distillation undervacuum. Colorless liquid & has pleasant fruity odor. Saponify the ester and identify geraniol & acetic acid. Perfume, cosmetic, and food industry. 1- Antimicribial. 2- Natural antioxidant, help to prevent cancer. 3- Anthelmintic principle of palm rose oil | |Linalyl acetate | | Lavender & bergamot oils F.D under high vacuum (hydrolysis in atmospheric pressure) Colorless liquid & has pleasant fruity odor of bergamot oil. Saponify the ester and identify linalool & acetic acid. Linalool is effective antimicrobial. 2- linalyl acetate is antispasmodic & act as fungicide. | - Other aliphaticesters : ## Esters of aromatic acid ### Table 2: Esters of aromatic acid | Vol oil | Structure | 2- Esters of Aromatic acid| |:---|:---|:---| |Benzyl benzoate | | Ylang ylang oil (Cananga spp, Family Anonaceae) Balsam tolu & Balsam peru By cooling the fraction containing the ester to low temp. Viscid oil, congeals at low temp to white crystals. Saponify the ester & identify benzyl alc & benzoic acid. 1- Fixative in perfume (low volatility). 2- Used to treat lice & Scabies infestations. The medicine is believed to be absorbed by lice & mites and to destroy them by acting on their nervous system. | | | Methyl salicylate COOCH3 OH | Oil of wintergreen (Gaultheria procumbens). Enzymatic hydrolysis followed by distillation Methyl salicylate occurs in the form of glucoside (gaultherin) in wintergreen, which by action of enzyme → liberate the ester Colorless oil, has powerful odor & flavor. 1- With aqueous FeCL3 → red violet colors. 2- Saponify the ester and identify methanol & salicylic acid. 3- Formation of derivatives wth: acetic anhydride, benzoyl chloride & phenyl isocyanate. • Gaultherin: 1- Used as a natural substitute of Aspirin. 2- Anti-inflammatory (cyclo-oxygenase ). Methyl salicylate: 1- antiseptic & antirheumatic. 2- local anesthetic agent & anticariogenic agent. | - Other aromatic esters: methyl cinnamate & benzyl cinnamate. ## Esters containing N2 ### Table 3: Esters containing N2 | Vol oil | Structure | 3- Esters containing N2 | |:---|:---|:---| | | Methyl anthranilate COOCH3 NH2 | Oil of neroli, Jasmine & ylang ylang. By shaking the oil with dil H2SO4 & the ester regenerated by NaOH. 1- Crystalline mass has powerful taste & special odor which in strong dilution resembles orange blossoms. 2- Has blue violet fluorescence (appear in any oil containing it). (m.p24-25) 6 (b.p→132) X. Formation derivatives [picrate needles[. Antifungal activity. | ## Determination of esters - The procedure based on saponifying the ester with standard alcoholic КОН: RCOOR' + KOH → reflux 1 hr → RCOO) K(+) + ROH - The amount of alkali consumed in saponification is determined by back titrating, the excess alkali with standardized acid. - From this, the % of ester is calculated. ### General precautions : 1. certain esters are not completely saponified in a period of one hour, ex: Salicylates & menthyl acetate that should be reflused for longer time. 2. In certain dark colored oils, it will be necessary to dilute the saponified oil with alcohol to specify the end point to the titration. # Aldehydes - The aromatic aldehydes of vol oil play important role in essential oils. - The lowest members of the aliphatic aldehydes: ex: formaldehyde & acetaldehydes occur in distillation water of vol oil. - Terpene aldehydes classified into: - A- Aliphatic. - B- Cyclic. - C- Aromatic. - D-Heterocyclic. ## Aliphatic terpene aldehydes ### Table: Aliphatic terpene aldehydes | Vol oil | Citroneallal (Rhodinal) | Citral | |:---|:---|:---| |Structure | | | |Source | d-form (most common) → oil of citronella, oil of lemon & Melissa officinalis, Family Labiatae. l-form Java in lemon oil. | 3,7 dimethyl- 2,6 octadiene-1al - زيادة • It occurs as mixture of 4 isomers. Present in oil of lemon grass (Poaceae), ginger root, Eucalyptus straigeriana, lemon, Citrus spp. | |Isolation | Through the formation of the crystalline bisulfite compound. Great care must be done in decomposing the bisulfite compound (by NaCO3 not NaOH) due to the instability of this aldehyde. Citronellal contains an ethylenic linkage & an aldehydic group → three different bisulfite compounds are possible: | | ### Table: Citronellal (Rhodinal) and Citral | Vol oil | Citronellal (Rhodinal) | Citral | |:---|:---|:---| |Isolation | Complete decomposition & regeneration: by treating with dilute acid or alkali (Na carbonate). | Regeneration carried out using NaOH & distillation under vacuum. (more stable towards the alkali). | |Precaution | Alkali affect the aldehyde cause resinification of the oil. Can be obtained from citral by reduction: | | |Synthesis | | | |Properties | Colorless liquid. It has strong tendency towards cyclization, in acidic media Resinify rapidly under the influence of alkali. | Slightly yellowish liquid & optically inactive. • It has tendency towards cyclization, in acidic media, give P-cymene • Oxidized by oxidizing agent (its yellow color is intensified) • Undergoes condensation with acetone: | |Identification | Through preparation of derivatives: Semicarbazone & 2,4 dinitro-phenyl hydrazones • Perfumes & scenting of soaps. • Natural insecticide and repellent for controlling red flour beetle. | • Used in perfumery & for synthesis of a-ionone & ẞ-ionone. 1- Sedative & relaxant & Estrogenic activity. 2- Antifungal & Anti-microbial. strong anti-fungal effect on Aspergillus flavus os Vi spores. | # Separation of Citronellal from citral - Tiemann's procedure: based on the fact that: - Citronellal → reacts only with conc solution of Na sulfite : - Citral reacts with dil solution - Gildemeister & Hoffmann's procedures: - Citronellal reacts with neutral Na sulfite & form hydrosulfonic derivatives, from which Citronellol can't be recovered. - N.B: 1- CO2 or an acid must be slowly added in sufficient quantities. - 2- The NaOH liberated during the reaction should be neutralized. - R-CHO + Na2SO3 + H2O → R-CH 애 + NaOH SO3 Na ↓ must be neutralized 503 Na - Separation of Citral a from Citral b - 1- Depending on the solubility of Na bisulfite complex →(Citral a is sparingly soluble in water while Citral b is readily soluble in water). - 2- Depending on the reaction with alkaline cyanoacetic acid (NCCH2COOH): -* Citral a is reacts more readily than Citral b. # B- Cyclic terpene aldehydes ### Table: B- Cyclic terpene aldehydes | Vol oil | Phellandral | Perillaldehyde | Safranal | |:---|:---|:---|:---| |Structure | | | | |Source | Several Eucalyptus spp | Oil of Perilla frutescens, Family Labiatae. | *Crocus sativus, Family Iridaceae *It has anti-inflammatory Potential & has strong anti-oxidative effect on CCl4 induced oxidative stress & inflammation in rats. 1- Antioxidant & radical scavenger. 2- Antidepressent & Anticonvulsant. 3- Cytotoxic towards cancer cell. | | Isolation | Form Na bisulfite complex, regenerated by alkali | | | |Properties | It is oil, Readily oxidized to • phellandric acid on exposure to air. * Antimicrobial activity. | When treated with NH2OH → it gives Perillatrine (Perilla sugar) that has 200 times sweet as sucrose * Recently: it of & used as sweetening agent. vaginal candidiasis | | | Uses | | | | - They are powerful broad-spectrum anti-infections, antibacterial, antiviral, antifungal, anti-parasite, immune system stimulant & general tonic. # C-Aromatic aldehydes ### Table: C-Aromatic aldehydes | Vol oil | Benzaldehyde | Cinnamic aldehyde | Vanillin | |:---|:---|:---|:---| | Structure | | | | |Source | * Present in the form of glucosides, ex: amygdalin in bitter almond, kernels (peach, apricot). | * In Cassia & cinnamon oils. * Isolated by formation of Na sulfite or bisulfite complex & regenerated by Na2CO3. 1- Yellow liquid. 2- has cinnamon odor. 3- It is partially oxidized to cinnamic acid when exposed to air. | * vanilla pods, balsam peru & clove oil as glucoside 1- Enzymatic hydrolysis or through bisulfite compound. 1- Has both aldehyde & phenol characters. 2- Crystalizes from hot water (colorless crystals ). 3- Has intense sweet odor & On careful heating → sublimated. 1- Acidic to litmus & by Formation of numerous derivatives. 2- With FeCL3 → blue color. * Flavor & perfumes. | |Isolation | | | | |Properties | * Amygdalin →split into benzaldehyde + Glu + HCN | | | |Identification | | | | |Uses | | | | ## Preparation of vanillin 1. From vanilla pods by extracting the powder with ether & purifying the residue & crystallized by alcohol. 2. By oxidation of liginin, • vanillin is formed in high yield. Curing process by careful heating: extraction Gluco vanillin enz vanillin + glucose. 3. From eugenol : - By Reimer Tiemann's reaction : Guaiacol - Vanillin + O-Vanillin # D-Heterocyclic aldehyde ### Table: D-Heterocyclic aldehyde | Vol oil | Furfural | |:---|:---| |Source | • Family Pinaceae | |Isolation | • By formation of Na bisulfite complex | |properties | • 1- Colorless liquid which darkens on exposure to air. 2- Reduces Fehling solution. | |Identification | • With aniline acetate → red color. 2- Formation of derivatives: Oxime & Phenyl hydrazone. | # Ketones - A-aliphatic ketones: Not commonly occur in vol oils. - B-Cyclic terpene ketones: - 1- Monocyclic: methone , carvone & diosphenol - 2- Bicyclic: Fenchone & camphor. ## Monocyclic terpene ketones ### Table: Monocyclic terpene ketones | Vol oil | Menthone | Carvone | Diosphenol | |:---|:---|:---|:---| |Structure | | | | |Source | * It exist in different modifications: d, I, dl d-form → oils of caraway & dill. l-form → oils of pennyroyal, peppermint (mentha pulegium). dl-form → spearmint oil (Mentha spicatà) dl-form → ginger grass oil. | | * Buchu leaves By cooling repeatedly to(-20) 1- Crystalline colorless sublimable. 2- Has camphor like odor. 3- Readily attacked by oxidizing agent | |Isolation | * Through its semicarbazone or oxime & regenerated by dil H2SO4. * Oily colorless liquid with peppermint odor & less cooling taste than 1-menthol. | 1- Colorless oil has caraway odor. 2- Congeals at low temp & reacts with NH4OH-HCL (at 75°C) → Estimation | | |Properties | | | With FeCL3 → intense green color Urinary antiseptic. | |Identification | 1- Flavoring, synthesis of menthol 2- ttt of mucopurulent infections (also carvone & fenchone). 3- Thiosemicarbazones & semicarbazone Derivatives has anti-HIV activity & acaricidal activity. 4- Penetration enhancer percutaneous absorption of tamoxifen (breast cancer) | 1- Carminative, in perfumes & soaps. 2- Synthesis of the terpenoid quassin. 3- Cyan-carvone → Synthetic derivatives has Anticonvulsant effect. | | |Uses | | | | ## Bicyclic terpene ketones ### Table: Bicyclic terpene ketones | Vol oil | Fenchone | Camphor | |:---|:---|:---| |Structure | | | |Source | * d-form → fennel oil & l-form → Thuja oil. | * d-form → Camphor tree, l-form → lavender & dl-form → Sage oil | |Isolation | | 1- By cooling or freezing. 2- By formation of complexes with strong acids. Ex: 80% H2SO4. Crystalline sublime & Doesn't combine with sodium bisulfite Natural camphor is while synthetic camphor is racemic. dl | |Properties | | | |Identification | * Through its semicarbazone & oxime derivatives. | * Through its oxime derivatives | |Uses | 1- Used as flavor in foods & perfumery. 2- N-acyl compound from fenchone has antituberculosis activity. | * Camphor might be safe & effective Penetration enhan cer For.transdermal.drug delivery. | # Methods for Separation of borneol from camphor: - Through formation of soluble ester with phthalic or succinic acid. - Through forming non-volatile esters with benzoic or stearic anhydride & removing camphor by distillation. - Converting camphor to its oxime which is soluble in 25% H2SO4. # In order to distinguish natural camphor from synthetic camphor: 1. Natural camphor + vanillin/HCL (1:100): at 30°C → yellow color, at 60°C → blue green color, at 75°C → indigo blue color. - Thịs color is due to impurities in the natural camphor & not given after repeated crystallization. synthetic camphor → no reaction. 2. Natural camphor is optically active (d-form) while synthetic camphor. (dl-form). 3. Synthetic camphor give (+ve) test for CL - A-Flame test: To detect the green flame of CL. - B-Combustion test: this is a more accurate test, - * The oil is deposited on filter paper disc & placed in porcelain dish upon which is inverted a beaker moistened on the inner surface. -* The paper is ignited & covered immediately with the beaker which is washed in test tube & tested for CL with AgNO3 → white ppt or turbidity. # Determination of aldehydes & ketones 1. **The bisulfite method:** - upon shaking a measured quantity of the oil with a hot aqueous solution Na bisulfite → form an addition compound which dissolves in the hot bisulfite solution. - The non-aldehydic portion of the oil separates as an oily layer, which can be measured in the graduated neck of cassia flask. - This type of assay is known as an absorption process. (mainly for aldehyde & some ketones). - **Application:** - 1- Determination of citral in lemongrass. - 2- Cinnamic aldehyde in cassia oil - 3-Benzaldehyde in bitter almond. - **Advantage:** Simple & Convenient. - **Disadvantage:** - 1- Water-soluble components or adulterants interfere. - 2-Cannot be used for most ketones. 2. **Hydroxylamine method:** - This method is based on the reaction of the aldehyde or ketone with hydroxylamine HCL & titration of HCL liberated by standard alkali solution. - **Advantage:** - 1- Applicable to all aldehydes & most ketones. - 2- A small amount of the oil is used. - 3- Reaction is rapids (15 min for aldehydes). - 4- Used for ketonic compounds that do not form bisulfite compounds such as menthone. - 5- Water-soluble non-carbonyl components → do not analyze as apparent carbonyl compounds (aldehydes & ketones). - **Disadvantage:** This method determines the total carbonyl components & cannot be used to determine individual components. 3. **Semicarbazone methods:** - This is gravimetric method based on precipitation of the ketone (or aldehyde) in the form of semicarbazone by reacting with semicarbazine HCL (semicarbazide) & weighing the semicarbazone. - This method used for the quantitative assay of camphor. 4. **Gas chromatography:** - Quantitative assay is based on area under the peak (AUC). - **Advantage:** - 1- Rapid. - 2- Accurate & sensitive. - 3- Allow the determination of individual carbonyl components as well as other non carbonyl components of the oil (over other methods) 5. **Phenyl hydrazine Method:** - This method is not commonly used today. - It has been used in the assay of citral in lemon oil. - It is now largely replaced by the hydroxylamine hydrochloride method.