New microsoft word documentDiscuss Phenols and their derivatives as Antiseptics


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New microsoft word documentDiscuss Phenols and their derivatives as Antiseptics

  1. 1. MSA University, Faculty of Pharmacy Organic Chemistry Department. 1- NAME OF THE ASSIGN : Discuss Phenols and their derivatives as Antiseptics 2- Course Code, PC 112 NAME : MOHMAEDADEL AFIFI ABDO ID:142311 FOR DR : NADIA ----
  2. 2. Phenol is the original antiseptic, old name carbolic acid. This was used by Lister, who discovered antiseptics. It works well but is rather toxic. If you react phenol with chlorine, then you get a Trichlorophenol, called TCP. This is pretty non-toxic and TCP is the most widely used phenol derivative used as an antiseptic today. There are many other halogenated phenol derivatives in use and these include Chlorocresol Chloroxylenol Chlorophene Hexachlorophane/hexachlorphene Triclosan Phenol was first extracted from coal tar, but today is produced on a large scale (about 7 billion kg/year) from petroleum. It is an important industrial commodity as a precursor to many materials and useful compounds.[4] Its major uses involve its
  3. 3. conversion to plastics or related materials. Phenol and its chemical derivatives are key for building polycarbonates,epoxies, Bakelite, nylon, detergents, herbicides such as phenoxy herbicides, and numerous pharmaceutical drugs. Although similar to alcohols, phenols have unique distinguishing properties. Unlike in alcohols where the hydroxyl group is bound to a saturated carbon atom,[5] in phenols the hydroxyl group is attached to an unsaturated ring such as benzene or other arene ring.[6] Consequently, phenols have greater acidity than alcohols due to stabilization of the conjugate base through resonance in the aromaticity. Properties Phenol is appreciably soluble in water, with about 84.2 g dissolving in 1000 mL (0.88 M). Homogeneous mixtures of phenol and water at phenol to water mass ratios of ~2.6 and higher are also possible. The sodium salt of phenol, sodium phenoxide, is far more water soluble Acidity Phenol is weakly acidic and at high pHs gives the phenolate anion
  4. 4. C6H5O− (also called phenoxide):[7] PhOH ⇌ PhO− + H+ (K = 10−10) One explanation for the increased acidity over alcohols is resonance stabilization of the phenoxide anion by the aromatic ring. In this way, the negative charge on oxygen is delocalized on to the ortho and para carbon atoms.[8] In another explanation, increased acidity is the result of orbital overlap between the oxygen's lone pairs and the aromatic system.[9] In a third, the dominant effect is the induction from the sp2 hybridised carbons; the comparatively more powerful inductive withdrawal of electron density that is provided by the sp2 system compared to an sp3 system allows for great stabilization of the oxyanion Phenoxide anion The phenoxide anion has a similar nucleophilicityto free amines, with the further advantage that its conjugate acid (neutral phenol) does not become entirely deactivated as a nucleophile even in moderately acidic conditions. Phenols are sometimes used in
  5. 5. peptide synthesis to "activate" carboxylic acids or esters to form activated esters. Phenolate esters are more stable toward hydrolysis than acid anhydrides and acyl halides but are sufficiently reactive under mild conditions to facilitate the formation of amide bonds Reactions Phenol is highly reactive toward electrophilic aromatic substitution as the oxygen atom's pi electrons donate electron density into the ring. By this general approach, many groups can be appended to the ring, via halogenation, acylation,sulfonation, and other processes. However, phenol's ring is so strongly activated—second only to aniline—that bromination or chlorination of phenol leads to substitution on all carbons ortho and para to the hydroxy group, not only on one carbon. When a mixture of phenol and benzoyl chloride when shaken in presence of dilute sodium hydroxide solution, phenyl benzoate is formed. This is an example of Schotten-Baumann reaction: C6H5OH + C6H5COCl → C6H5OCOC6H5 + HCl
  6. 6. Phenol is reduced to benzene when it is distilled with zinc dust or its vapour is passed over granules of zinc at 400 °C:[15] C6H5OH + Zn → C6H6 + ZnO Production Because of phenol's commercial importance, many methods have been developed for its production. The dominant current route, accounting for 95% of production (2003), involves the partial oxidation of cumene (isopropylbenzene) via the Hock rearrangement:[4] C6H5CH(CH3)2 + O2 → C6H5OH + (CH3)2CO Compared to most other processes, the cumene-hydroperoxide process uses relatively mild synthesis conditions, and relatively inexpensive raw materials. However, to operate economically, there must be demand for both phenol, and the acetone by-product. An early commercial route, developed by Bayer and Monsanto in the early 1900s, begins with the reaction of a strong base with benzenesulfonate:[16]
  7. 7. C6H5SO3H + 2 NaOH → C6H5OH + Na2SO3 + H2O Other methods under consideration involve: hydrolysis of chlorobenzene, using base or steam (Raschig–Hooker process):[17] C6H5Cl + H2O → C6H5OH + HCl Uses The major uses of phenol, consuming two thirds of its production, involve its conversion to precursors to plastics. Condensation with acetone gives bisphenol-A, a key precursor to polycarbonates and epoxide resins. Condensation of phenol, alkylphenols, or diphenols with formaldehyde gives phenolic resins, a famous example of which is Bakelite. Partial hydrogenation of phenol gives cyclohexanone, a precursor to nylon. Nonionic detergents are produced by alkylation of phenol to give thealkylphenols, e.g., nonylphenol, which are then subjected to ethoxylation.[4] Phenol is also a versatile precursor to a large collection of drugs
  8. 8. Toxicity Phenol and its vapors are corrosive to the eyes, the skin, and the respiratory tract.[37] Repeated or prolonged skin contact with phenol may cause dermatitis, or even second and third-degree burns.[38] Inhalation of phenol vapor may cause lung edema.[37] The substance may cause harmful effects on the central nervous system and heart, resulting in dysrhythmia, seizures, and coma.[39] The kidneys may be affected as well. Long-term or repeated exposure of the substance may have harmful effects on the liver and kidneys.[40] There is no evidence that phenol causes cancer in humans.[41] Besides its hydrophobic effects, another mechanism for the toxicity of phenol may be the formation of phenoxyl radicals.[42]