Phenol

9 Key excerpts on "Phenol"

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  eBook - PDF

  Textbook of Chemical Peels

  Superficial, Medium, and Deep Peels in Cosmetic Practice

  • Philippe Deprez, Philippe Deprez(Authors)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  25 Phenol Chemistry, formulations, and adjuvants CHEMISTRY OF Phenol As a class, Phenols are compounds in which a hydroxy group is attached to a benzene ring. The name Phenol also is used to refer specifically to the simplest compound in this group, which is also known as hydroxybenzene, benzenol, or carbolic acid (Figure 25.1). 1 Phenol has a molecular weight of 94.11, a spe-cific gravity of 1.071, and a boiling point of 182°C. It can react vigorously or even violently with other compounds, including formaldehyde, acetaldehyde, and trifluroacetic acid, as well as aluminum chloride, nitrobenzene, some nitrates and nitrites, and other oxidizing agents. Phenol crystals are white or pink, and melt at 41°C. Most commercial Phenol has a purity of 98%, but 100% pure Phenol is obtainable. 2 Phenol was formerly obtained from coal tar but is now made by hydrolyzing chlorobenzene at 350°C or, more frequently, by air oxidation of cumene 3 and treatment of the resulting cumene hydroperoxide to yield Phenol and acetone (Figure 25.2). Estimates of the amount of Phenol produced worldwide vary, but since 1980 more than 5,000,000 tons have been produced. Phenols may have more than one hydroxy group attached to the same benzene ring—for example, the three iso-meric 4 dihydroxybenzenes catechol ( ortho -dihydroxybenzene or 1,2-benzenediol), resorcinol ( meta -dihydroxybenzene or 1,3-benzenediol), and hydroquinone ( para -dihydroxybenzene or 1,4-benzenediol); see Figure 25.3. Molecules that have a single benzene ring with one or more hydroxy substituents are known as “simple Phenols.” Examples are Phenol itself and the three dihydroxybenzenes mentioned in the previous paragraph, as well as the cresols (discussed later). There are also “diPhenols” (Figure 25.4) and polyPhenols. PolyPhenols are complex molecules containing several benzene rings with one or more hydroxy substituents. They are widespread in nature, often lending plants their color.

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  Pharmaceutical Chemistry E-Book

  • David G. Watson(Author)
  • 2011(Publication Date)
  • Churchill Livingstone

    (Publisher)

  Ka value 10.0 and is soluble 1 in 20 in water. It is still used occasionally in the form of an oily injection, because of its caustic nature, to promote sclerosis in the treatment of haemorrhoids.

  Figure 5.10 Phenols.

  When additional hydroxyl groups are attached to the benzene ring a range of fairly reactive compounds, e.g. catechol, hydroquinone and pyrogallol (Fig. 5.10 ) results. These compounds, unlike ordinary alcohols, are all readily oxidised and the oxidation products (quinones) are also highly reactive with biological structures and certainly not desirable as the products of drug metabolism. The Phenolic hydroxyl group is widely found in natural products such as tyramine, dopamine which is used therapeutically, and in Phenolic pigments such as quercetin which is a dietary antioxidant compound (Fig. 5.10 ). Phenolic acids occur widely in the diet; for example, the rich content of Phenolic acids in cranberry juice is the basis for its mild antibacterial action in treating cystitis. Phenolic groups can have a strong effect on biological activity. The presence of a catechol group is critical for biological activity in noradrenaline; p -octopamine lacks the m -hydroxyl group found in noradrenaline (Fig 5.11 ) and has little activity at noradrenergic receptors. However, by a quirk of nature it fulfils the role of noradrenaline in the nervous systems of insects.

  Figure 5.11 Biologically active Phenols.

  Phenol acidity and antibacterial action

  Unlike alcohols, which are neutral, Phenols are weakly acidic. The acidity of the hydroxyl group results from the electron withdrawing effect of the aromatic ring which weakens the OH bond. The acidic strength of the Phenol increases with the strength of electron withdrawal. Thus electron withdrawing substituents such as nitro or chloro groups increase the acidity of the Phenol (Fig. 5.12 ). The effects of such substituents are greatest in the ortho and para positions. The amphiphilic nature of Phenols means that they are surface active and can absorb on membrane surfaces such as bacterial membranes. The more acidic Phenols have stronger antibacterial action and chloroxylenol is commonly used in disinfectants, ethylparaben is used as a preservative in liquid formulations and triclosan (Fig. 5.12

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  Reducing Agents in Colloidal Nanoparticle Synthesis

  • Stefanos Mourdikoudis(Author)
  • 2021(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  11 The acidic character as well as the chemical and physical properties of Phenol derivatives may differ as a function of the number of hydroxyl and additional functional groups.

  It is important to understand the properties of the Phenol derivative chosen for the synthesis in order to optimize the reaction conditions and achieve uniform and well-distributed MNPs with controlled size, shape, and morphology. In general, as the number of –OH groups increases, both the boiling and the melting points increase, as well as the water solubility, due to the strong intermolecular forces (e.g. hydrogen bonding). A few exceptions to this rule are observed: Phenol, with one hydroxyl group, hydroquinone, with two, and phloroglucinol, with three, have water solubilities of 83 g L−1 , 72 g L−1 , and 10 g L−1 , respectively. This decrease in solubility is a result of the formation of symmetrical and rigid molecule networks via hydrogen bonds in these molecular structures, which prevent the penetration of the solvent used in the reaction.

  12 ,13

  In addition, if the ring has other substituents such as carboxyl (–COOH), nitro (–NO2 ), and amino (–NH2 ) groups, their close proximity to the hydroxyl group will further enable the hydrogen bonding in the molecule, lessening the solvation of the Phenol derivative and thus making it less water soluble in the reaction medium (e.g. ortho substitution compared to para substitution).

  14

  The pK a value is the negative log of the acid dissociation constant and thus an indication of the acid strength of the molecule. Introduction of more –OH groups or other electron-donating substituents such as amino (–NH2 ), alkyl (–R), or alkoxy (–OR) groups will alter the charge density on the aromatic ring in such a way that its pK a value will increase as a result. Therefore, Phenols with such substituents are less acidic compared to unsubstituted Phenols or to those with electron-withdrawing ones such as halides, –NO2 , and –COOH groups. It is also important to note that as the number of chlorine atoms attached to the aromatic ring increases, the acidity of the molecule increases with the decreasing pK a

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  Chemistry and Biochemistry of Flavoenzymes

  Volume II

  • Franz Muller(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  Eur. J. Biochem., 170, 343, 1987. With permission.)

  IV. Biological Significance

  A. Phenol as Carbon and Energy Source

  Phenolic compounds are widely distributed in nature, deriving mainly from wood lignins. Their mineralization is vital to a proper functioning of the carbon cycle. Hence, the great importance of those flavoprotein hydroxylases, which initiate the degradation of aromatic acids, which are decomposition produets of lignins. The process of lignin degradation dates back to the cambrian era, when woody plants began to appear, some 370 million years ago. The aromatic hydroxylases acting on Phenolic acids must thus have evolved about that time. Phenol and its simple methyl, amino, or halogen derivatives are toxic produets of industriai origin. It is ali the more remarkable that their degradation is initiated by Phenol hydroxylases which, albeit in many respects similar to those involved in lignin degradation, have no aromatic substrates in common.

  Higher organisms remove toxic aromatic substances using monooxygenases of the P-450 type. These are mere detoxification processes, in which the carbon and energy content of such substances is lost. By contrast, microbes detoxify aromatic substances using flavoprotein hydroxylases and, in most cases, they also manage to fully utilize their content of carbon and energy. The efficiency of Phenol utilization by the lower eukaryote, T. cutaneum, is remarkable. In chemostat cultures, the celi yields on Phenol are comparable to those on such easily utilized carbon sources as glucose or acetate. The “maintenance coefficient” on Phenol as a sole carbon source is extremely low, indicating very efficient energy coupling.55 In steady-state continuous cultures on Phenol without carbon limitation, there is a considerable increase in the level of several intracellular enzymes, including those related to the Krebs cycle and to generation of reducing power.55 In the presence of Phenol, the organism even develops a specific active transport system to bring this compound into the cell.

  56 ,57

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  Biomass, Biofuels, Biochemicals

  Recent Advances in Development of Platform Chemicals

  • S. Saravanamurugan, Hu Li, Anders Riisager, Ashok Pandey(Authors)
  • 2019(Publication Date)
  • Elsevier

    (Publisher)

  It also serves as a precursor to a large array of drugs, herbicides, cosmetics (including sunscreens, hair coloring, and skin lightning preparations), and pharmaceuticals [ 6, 7 ]. Aromatic Phenols are naturally reactive compounds; they are acidic in nature owing to the presence of an OH group. When reacting with metals, they form chelate complexes and are easily oxidized and form polymers. According to a 2006 survey, the global production of Phenols was 80 million tons, but more than 95% was produced from fossil-derived benzene by the cumene process [8]. During lignin degradation, catalytic reduction reactions aim to remove the extensive functionality of lignin subunits to generate simpler monomeric compounds, including Phenols, benzene, toluene, and cyclohexane, which can be further hydrogenated to alkanes (carbon atoms C7–18) via coupling reactions or used as platform chemicals in an appropriate reaction environment [ 9, 10 ], as displayed in Fig. 18.1. To a larger extent, cyclohexanol, cyclohexanone, and cyclohexane are considered to be valuable products in the application of direct blending with petroleum fuels [11]. Conventionally, lignin valorization is conducted through thermal hydrogenolysis (depolymerization), which could be a base-catalyzed, acid-catalyzed, metallic-catalyzed, and ionic liquid–assisted depolymerization for the synthesis of various Phenolics [ 6, 12, 13 ]. Although lignin forms a large proportion of the nonfood biomass, which is categorized as eligible for the production of renewable and carbon-neutral liquid fuels and chemical compounds, its separation from covalently linked materials such as cellulose and hemicellulose is a major technical hurdle that needs to be overcome for cost-effective production [14]. Compared with many bulk aromatic chemicals used in the chemical industry, the aromatic units that make up lignin are highly functionalized (i.e., oxygenated and alkylated) [15]

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  The Chemistry of Phenols

  • (Author)
  • 2004(Publication Date)
  • Wiley-Interscience

    (Publisher)

  The significance of the reaction of Phenol with hydrogen has a number of important facets. First, the selective hydrogenation of Phenol yields cyclohexanone, which is a key raw material in the production of both caprolactam for nylon 6 and adipic acid for nylon 6 771 . Second, due to the fact that Phenol is an environmental toxin 772 and Phenolic waste has a variety of origins from industrial sources including oil refineries, petrochemical units, polymeric resin manufacturing and plastic units 773 , catalytic hydrogenation of Phenol is nowadays the best practicable environmental option 774 . Cl Cl C C O C H H C N C C H C C H C C Cl H H C H C Cl Cl 1.795 117.8 2.580 1.745 1.739 1.332 153.0 1.005 H FIGURE 57. The complex of pentachloroPhenol with 2-methylpyridine optimized at the B3LYP/6-31G(d) computational level. Bond lengths are in ˚ A, bond angles in deg 1. General and theoretical aspects of Phenols 179 The behaviour of the tyrosyl radicals involved in different processes and environ- ments is not yet well understood 491, 546, 775 . Relatively little is known about the structure and selectivity of aryloxylium cations (Ar−O + ) that are produced in the Phenolic oxi- dation reactions and implicated in biological processes such as isoflavone synthesis 776 . The thermochemistry 197 which is relevant to the antioxidant properties of Phenols as well as the solvent effects on their reactivity 777 – 780 remain also a largely under-explored topic. Finally, the structure of Phenol dimers and oligomers 781 or even of some specific Phenols 782 also deserve more attention. We expect that these problems will be subjects for theoretical research in the coming years. VII. ACKNOWLEDGEMENTS The authors gratefully thank Therese Zeegers-Huyskens, Asit Chandra, Sergei Bureiko, Kiran Boggavarapu, Alexander Koll, Zdislaw Latajka, Noj Malcolm, Bernard Silvi, Lucjan Sobczyk, Raman Sumathy and Georg Zundel for warm and useful discussions and suggestions.

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  Bio-Based Solvents

  • François Jérôme, Rafael Luque, François Jérôme, Rafael Luque(Authors)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  Figure 7.1 ) [16, 17]. Particularly, the short-chain alkylPhenols can be manufactured directly from lignin by using recently developed technologies [16, 17]. The long-chain alkylPhenols can also be produced from biomass in a few steps. However, thus far, limited studies have focused on using alkylPhenols as bio-based solvents. Hence, this chapter will discuss the main properties of alkylPhenols, their production and their utilization as solvents. Finally, the stability and toxicity aspects of alkylPhenols are highlighted and an outlook is provided.

  7.2 Properties of AlkylPhenols

  AlkylPhenols are a family of Phenol-derived organic compounds obtained by replacing one or more of the ring hydrogens with alkyl groups [18, 19]. In this chapter, we mainly discuss the mono-alkylated Phenols. Pure alkylPhenols appear colourless or white to a pale yellow, and have a Phenol-type odour. They show the same sensitivity to oxygen as Phenol, in the sense that oxidation can cause discoloration. The properties of alkylPhenols are strongly affected by the size and the configuration of the alkyl group. The physical form of alkylPhenols at 25°C is determined by the type of alkyl group and the mutual positions of the alkyl and hydroxyl groups. For example, ortho-cresol and Phenol are solids, whereas meta-cresol is a liquid. The boiling points of alkylPhenols increase continuously with increasing size of the alkyl group, hence molecular weight (MW) (Figure 7.2 ). The para-alkylPhenols have higher boiling points than the corresponding ortho-isomers. However, the difference in boiling points between the meta- and para-isomers is very small, which leads to difficulties in separating them by distillation. The n-alkylPhenols have higher boiling points than the corresponding iso-alkylPhenols. The solubility of alkylPhenols in water decreases logarithmically with increasing size of the alkyl group (Figure 7.2

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  Understanding Advanced Organic and Analytical Chemistry

  The Learner's ApproachRevised Edition

  • Kim Seng Chan, Jeanne Tan;;;(Authors)
  • 2016(Publication Date)
  • WS EDUCATION

    (Publisher)

  π-electron cloud of the benzene ring. As a result, the lone pair of electrons on the O atom can delocalize into the benzene ring. This results in the C–O bond bearing a partial double bond character and thus being stronger than the C–O bond in an aliphatic alcohol. In addition, due to this delocalization, the carbon atom that bears the −OH group is less electron-deficient, hence less susceptible to nucleophilic attack.

  The reactions that Phenol undergoes can be classified into one of the following:

  • Reactions involving cleavage of O–H bond

  • Electrophilic substitution of the parent benzene ring

  8.7.1 Acid-Base Reaction with Strong Bases and Reactive Metals

  Phenol reacts with strong bases such as NaOH and reactive metals. However, it is not strongly acidic enough to react with carbonates.

  8.7.2 Formation of Esters with Acid Chlorides — Acylation vis Nucleophilic Substitution/ Condensation

  Phenol reacts with acid chloride to form a Phenolic-ester, but it does not react with carboxylic acids to generate the Phenolic-ester.

  Q:

  Why can alcohol react with carboxylic acid to form an ester but not Phenol?

  A:

  The reaction of an alcohol with carboxylic acid to form an ester is a nucleophilic substitution as shown:

  An alchohol’s lone pair of electrons is especially available due to the electron donating effect of the alkyl group. As for Phenol, the lone pair of electrons on the O atom is not readily available since they can delocalize into the benzene ring. Hence, Phenol is not a good nucleophile as compared to alcohol. But by converting the carboxylic acid to a more reactive acid chloride, we can make Phenol react with acid chloride to form an ester. In addition, Phenol can be made a better nucleophile by converting it to the phenoxide ion upon treatment with NaOH(aq). So, take note that to obtain Phenolic ester, it is not necessary to convert the Phenol to phenoxide first!

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  Principles of Organic Chemistry

  • Robert J. Ouellette, J. David Rawn(Authors)
  • 2015(Publication Date)
  • Elsevier

    (Publisher)

  8

  Alcohols and Phenols

  8.1 The Hydroxyl Group

  Families of organic compounds that have functional groups containing oxygen include alcohols, Phenols, ethers, aldehydes, ketones, acids, esters, and amides. Alcohols and Phenols both contain a hydroxyl group (–OH). A hydroxyl group is also present in carboxylic acids, but it is bonded to a carbonyl carbon atom. As a result, the chemistry of carboxylic acids, the subject of Chapter 12 , is substantially different from the chemistry of alcohols and Phenols. Alcohols and Phenols can be viewed as organic “relatives” of water in which one hydrogen atom is replaced by an alkyl group or an aryl group. Alcohols contain a hydroxyl group bonded to an sp3 -hybridized carbon atom. Phenols have a hydroxyl group bonded to an sp2 -hybridized carbon atom of an aromatic ring.

  Common Names of Alcohols

  The common names of alcohols consist of the name of the alkyl group (Section 3.3 ) followed by the term alcohol . For example, CH3 CH2 OH is ethyl alcohol and CH3 CH(OH)CH3 is isopropyl alcohol. Other common names are allyl alcohol and benzyl alcohol, whose structures are shown below.

  The IUPAC system of naming alcohols is based on the longest chain of carbon atoms that includes the hydroxyl group as the parent chain. The parent name is obtained by substituting the suffix -ol for the final -e of the corresponding alkane. The IUPAC rules are as follows:

  1.  

  The position of the hydroxyl group is indicated by the number of the carbon atom to which it is attached. The chain is numbered so that the carbon atom bearing the hydroxyl group has the lower number.

  The longest chain that contains the hydroxyl group has 4 carbon atoms. An OH group is at C-2 and a methyl group is at C-3. So, the name is 3-methyl-2-butanol

  2.  

  When the hydroxyl group is attached to a ring, the ring is numbered starting with the carbon atom bearing the hydroxyl group. Numbering continues in the direction that gives the lowest numbers to carbon atoms with substituents such as alkyl groups. The number 1 is not used in the name to indicate the position of the hydroxyl group.

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