######################################## #Written by David Tam, 1994. # #davidkftam@netscape.net Copyright 1999# ######################################## Benzaldehyde Chemical Information - OAC Chemistry ISP ===================================================== Introductory Information (*2, 4, 7) ======================== - other names: benzoic aldehyde - physical state: liquid - appearance: clear to yellow - odor: almond - yellow organic oil that has a burning aromatic taste - undergoes reactions characteristic of aldehydes - becomes yellowish in keeping Molecular Formula (*2, 7, 8) ================= C7H6O or C6H5CHO Molecular Mass (*2, 9) ============== 106.13 g/mol Percentage Composition: ======================= C= 79.22%, H= 5.70%, O= 15.08% Structural Formula (*2, 8) ================== O " " H C-----H \ | \ | C===========C / \ / \ H-----C C-----H \\ // \\ // C-----------C / \ / \ H H Bond Angles and Shape (*1, 11) ===================== All bond angles are at 120 because all bonds form trigonal co-planars. Solvents for the Substance (*2, 7, 8, 10) ========================== Soluble in 250 parts water (0.3%) Miscible with alcohol, ether, fixed and volatile oils. Uses (*2, 4, 7, 8) ==== 1. flavoring agent (almond) 2. intermediate in chemical synthesis 3. manufacture of dyes, perfumery, cinnamic and mandelic acids 4. aromatic alcohols 5. solvent for oils 6. benzoic acid 7. pharmaceuticals 8. photographic chemicals 9. antibiotics Sources, Synthesis, and Derivation (*2, 4, 3, 7, 8) ================================== 1. may be synthesized by usual methods of aldehyde synthesis 2. extraction from kernels of bitter almonds 3. made synthetically from benzal dichloride and lime 4. air oxidation of toluene, with uranium and molybdenum oxides as catalysts 5. prepared industrially by hydrolysis of dichloromethyl benzene (also known as benzal dichloride) 6. benzoic acid mixed with LiAlH4 and water (as catalysts), forming 81% benzyl alcohol; benzyl alcohol mixed with CH2Cl2 and (C5H5N2)CrO3 (as catalysts) forming 89% benzaldehyde. One method of synthesis: ======================== C6H5CH3 + Cl2 ---> C6H5CHCl2 C6H5CHCl2 + 2H2O---> C6H5CH(OH)2 + 2HCl C6H5CH(OH)2 ---> C6H5CHO + H2O Purification Procedure (*8) ====================== Usually contaminated with chlorides, method of purification: rectification Density (*2, 8, 9) ======= - approx. 1.0 g/mol - specific gravity = 1.04 (compared to water) - vapor density (air = 1) = 3.7 approx - weight of liquid = 1.04 Kg/L Melting & Boiling Points (*2, 5, 7, 8, 10) ======================== - freezing / melting point = -56.6 C - boiling point = 179 C - flash point = 64.4 C - auto-ignition temp = 191.6 C - heat of vaporization = 361.8 J/g (int) - specific heat = 0.428 (liquid) - vapor pressure = 1 mm Hg Standard Enthalpy of Formation: =============================== (at 298.15K) liquid= -87.0 J/mol gas= -36.7 J/mol - standard entropy= 221.2 J/mol @ 298.15K - heat capacity= 172.0 J/mol @ constant pressure, 298.15K Index of refraction (*2, 8) =================== 1.5456 at 20 C in sodium light Fire, Explosion Hazard (*9, 10) ====================== - WHMIS class B and D2[(flammable) (poisonous, infectious)] - moderate fire hazard with exposure to heat or flame - combustible liquid - extinguished with CO2, dry chemicals, alcohol foam - not compatible with oxidizing materials - alkalies promote oxidation - reduction Hazardous Combustion Products: ============================== 1. carbon dioxide 2. carbon monoxide Biological Effects on Humans (*2, 9, 10) ============================ eyes- vapor causes irritation skin- prolonged exposure causes irritation - may cause contact dermatitis - allergenic inhalation- vapor irritates nose, throat ingestion- harmful - can cause convulsions - in high doses, CNS depression Over Exposure: ============== Inhalation of vapors may cause headache, nausea, dizziness, fatigue and weakness in arms and legs. Lethal Dosage: ============== 1300 mg/Kg for 50% of tested rats & guinea pigs tested ============================================================================== REPORT ====== The benzaldehyde molecule, an aromatic, organic compound, consists of a benzene ring structure (C6H6), with an aldehyde functional group attached to this ring.1 The basic benzene ring consists of six carbons attached in a circular manner, with a hydrogen at the end of each carbon, and with double bonds occurring at every other carbon-to-carbon bond.(1) The formation of benzaldehyde is accomplished by substituting one of hydrogen atoms attached to a carbon with the aldehyde functional group. The carbon atom forms 3 sp2 hybrid orbitals, bonding to two carbons, and one hydrogen.(1) This leaves one unhybridized p-orbital for each carbon.(1) Pi-bonds form above and below the plane, resulting in two doughnut-shaped electron clouds above and below the ring structure.(1) Because of this, the benzene ring is a planar (flat) molecule.(1,3) The attachment of the aldehyde by a carbon-to-carbon single bond allows for that functional group to rotate freely.(11) A benzene ring is a non-polar molecule, but with the addition of the aldehyde functional group, benzaldehyde is a polar molecule.(1,11) The slightly negative end is located around the oxygen atom of the functional group, and the slightly positive end is located at the benzene ring structure.(11) The electronegativity difference between the carbon and the oxygen is 0.89, resulting in a 19% ionic character.(11) A difference of 0.35 between carbon and hydrogen creates an ionic character of only 3%.11 The intermolecular force of dipole-dipole attraction holds this liquid together.(11) Because of the polar nature of the molecule, it has a low melting point of -56.5 C, a boiling point of 179 C, and a solubility of about 0.3% in water.(10) This liquid is combustible, with an auto-ignition temperature of 191.6 C, producing carbon monoxide and carbon dioxide.(9) It can be oxidized by air and other oxidants.(10) Because of the benzene ring structure, the molecule is aromatic, with a distinct almond-like odour.(1,7) Specific rotation and optical density of the molecule was not listed, though it was available for other substances. However, the index of refraction was available; 1.5456 at 20 C in sodium light.(2) ============================================================================== Bibliography ============ 1. Brady, James E. and John R. Holum. Fundamentals of Chemistry (3rd Ed). ------------------------- Toronto: John Wiley & Sons, Inc., 1988. 2. Budavar, Susan, ed. The Merck Index (11th Ed). --------------- Rahway: Merck & Co., Inc., 1989. 3. Carey, Francis A. Organic Chemistry (2nd Ed). ----------------- Toronto: McGraw-Hill, Inc., 1992. 4. Daintith, John Ph.D., ed. The Facts on File Dictionary of Chemistry. ----------------------------------------- New York: Charles Letts & Co., Ltd., 1988. 5. Dean, John A. ed. Lange's Handbook of Chemistry (11th Ed). ----------------------------- Toronto: McGraw-Hill Book Company, 1973. 6. Lide, David R., ed. Handbook of Chemistry and Physics (74th Ed). --------------------------------- London: CRC Press, Inc., 1993. 7. Parker P. Sybil ed. McGraw-Hill Dictionary of Chemistry. ----------------------------------- Toronto: McGraw-Hill Book Company, 1984. 8. Sax, Irving N. and Richard J. Lewis, Sr. Hawley's Condensed Chemical Dictionary (11th Ed). -------------------------------------- New York: Van Nostrand Reinhold, 1987. 9. "Benzaldehyde." Product Information Sheets Science (Vol 1) ---------------------------------- Peel Board of Education. 10. "Benzaldehyde - Card 112." Chemical Hazard Cards For Chemicals and --------------------------------------- Biologicals Used in School (Vol 1) Scarborough Board of Education, 1986. -- ------------------------ 11. Self-determined