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Hydroxy derivatives of hydrocarbons (alcohols, phenols, ethers) and sulfur analogues: Bonding system characterization. Physical properties. Acidbase properties, the structural determinants of acidity. Theirs reactions connected with their nucleophilic properties (alkylation, acylation, sulphonic acid, producing inorganic esters), alcohols, acid-catalyzed conversion. Oxidation of alcohols and phenols. Ethers properties, cleaved of ethers. Special bonding systems of ethers (epoxides and hemiacetals, acetals and enol ethers) and their chemical reactions. Their synthesis. Grouping of compounds with C-OH, C-O-C, C-SH and C-S-C bonds Starting point: classical valence theory: Formally - a water/a hydrogen sulphide is substituted with hydrocarbon radicals BUT! for sulphur empty d orbitals, S = O bond is established ("four and six valence" sulphur!) 1-C-OH bonded compounds (alcohols, phenols) according to the hybrid status of the pillar carbon: alcohols (R-OH): sp3 carbon phenols, enols (Ar-OH, C = C-OH): sp2 carbon - not arbitrary, different bonding! ethanol phenol vinyl alcohol according to the order of sp3 carbon atoms (alcohols): primary (1°), secondary (2°), tertiary (3°) similarity to the halogen derivatives according to the number of hydroxyl groups (diol, triol, polyol) in case of diols: according to their position to each other: geminal, vicinal, disjunct according to the nature of the hydrocarbon group: saturated / unsaturated / acyclic / cyclic n1 Nomenclature Functional class nomenclature Functional class names of alcohols are derived by naming the alkyl group that bears the hydroxyl substituent (±OH) and then adding alcohol as a separate word. The chain is always numbered beginning at the carbon to which the hydroxyl group is attached. Substitutive nomenclature Substitutive names of alcohols are developed by identifying the longest continuous chain that bears the hydroxyl group and replacing the -e ending of the 5-Chloro-2-methylheptane corresponding alkane by the suffix -ol. The position of the hydroxyl group is indicated by number, choosing the sequence that assigns the lower locant to the carbon that bears the hydroxyl group. Hydroxyl groups take precedence over (“outrank”) alkyl groups and halogen substituents in determining the direction in which a carbon chain is numbered. Trivial names (common names) Several alcohols are commonplace substances, well known by common names that reflect their origin (wood alcohol, grain alcohol) or use (rubbing alcohol). Wood alcohol is methanol (methyl alcohol, CH3OH), grain alcohol is ethanol (ethyl alcohol, CH3CH2OH), and rubbing alcohol is 2-propanol [isopropyl alcohol, (CH3)2CHOH]. Glycerol (glycerin, propane-1,2,3-triol), glycol (ethylene glycol, ethane-1,2-diol). Classification of C-OH, C-O-C, C-SH and C-S-C compounds 2. 2. C-O-C compounds (ethers) According to the linked groups: symmetrical and non-symmetrical (mixed) ethers According to the hydrocarbon group - Aliphatic ethers (R-O-R, R-O-R1) - Aliphatic-aromatic ethers (R-O-Ar) - Aromatic ethers (Ar-O-Ar1 + heteroaromatic analogues) - Specific, other ethers different (higher) reactivity enol ethers [-C = C-OR (Ar)] Special types of ether Ether derivatives of geminal diols Cyclic ethers epoxides (oxiranes) special compounds: different reactivity than cyclic ether hemiacetal acetal Similarity to aldehydes and ketones orthoester Relation to carboxylic acids 3. C-O-O-H, C-O-O-R compounds Formally, the alkylated / arylated derivatives of hydrogen peroxide Nomenclature of ethers Substitutive IUPAC nomenclature Ethers are named, in substitutive IUPAC nomenclature, as alkoxy derivatives of alkanes. ONLY alkoxy / aryloxy prefix + base carbon chain (+ local number multiplier members) Functional class IUPAC nomenclature Functional class IUPAC names of ethers are derived by listing the two alkyl groups in the general structure ROR in alphabetical order as separate words, and then adding the word “ether” at the end. When both alkyl groups are the same, the prefix di- precedes the name of the alkyl group. Ethers are described as symmetrical or unsymmetrical depending on whether the two groups bonded to oxygen are the same or different. Unsymmetrical ethers are also called mixed ethers. Diethyl ether is a symmetrical ether; ethyl methyl ether is an unsymmetrical ether. Nomenclature of ethers 2. Cyclic ethers have their oxygen as part of a ring—they are heterocyclic compounds Several have specific IUPAC names. trivial names, additive nomenclature, Hantzsch-Widman nomenclature Hantzsch-Widman nomenclature: (additive nomenclature) (trivial names) (trivial names) In each case the ring is numbered starting at the oxygen. The IUPAC rules also permit oxirane (without substituents) to be called ethylene oxide. Tetrahydrofuran and tetrahydropyran are acceptable synonyms for oxolane and oxane, respectively. Many substances have more than one ether linkage. Two such compounds, often used as solvents, are the diethers 1,2-dimethoxyethane and 1,4-dioxane. Diglyme, also a commonly used solvent, is a triether. 4. Compounds with C-S-H, C-S-R bonds (sulfur analogs of alcohols , phenols and ethers) In close analogy to the oxygen-containing analogues - thioalcohols, thiophenols, thioethers thioalcohol thiophenol sulfide (thioether) R1=R2 or R1≠R2 disulfide if n>2 polysulfide different from oxygen Derivatives with more than two ligands sulfinyl group sulfonyl group Relationship with sulfones according to the binding system, chemically similar to carboxylic acids Nomenclature of thiols Substitutive IUPAC names Thiols are given substitutive IUPAC names by appending the suffix -thiol to the name of the corresponding alkane, numbering the chain in the direction that gives the lower locant to the carbon that bears the ―SH group. The final -e of the alkane name is retained. When the ―SH group is named as a substituent, it is called a mercapto group. It is also often referred to as a sulfhydryl group, but this is a generic term, not used in systematic nomenclature. At one time thiols were named mercaptans. Thus, CH3CH2SH was called “ethyl mercaptan” according to this system. This nomenclature was abandoned beginning with the 1965 revision of the IUPAC rules but is still sometimes encountered, especially in the older literature. aromatics: thiophenol-based nomenclature Nomenclature of sulfides Substitutive nomenclature of sulfides The sulfur analogs (RS―) of alkoxy groups are called alkylthio groups. The first two of the following examples illustrate the use of alkylthio prefixes in substitutive nomenclature of sulfides. Prefixes: alkylthio/alkylsulfanyl, arylthio/arylsulfanyl, alkylpolythio Functional class IUPAC names of sulfides Functional class IUPAC names of sulfides are derived in exactly the same way as those of ethers but end in the word “sulfide.” hydrocarbon group names + sulfide, disulfide, polysulfide suffix Sulfur heterocycles have names analogous to their oxygen relatives, except that ox- is replaced by thi-. Thus the sulfur heterocycles containing three-, four-, five-, and sixmembered rings are named thiirane, thietane, thiolane, and thiane, respectively. Substitutive nomenclature: Functional class IUPAC names: Nomenclature of sulfoxides and sulfones Substitutive nomenclature prefix: alkylsulfinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl Functional class nomenclature hydrocarbon group names + sulfoxide / sulfone suffix Additionally: Compound Name + S-oxide / S, S-dioxide suffix Substitutive nomenclature: Functional class nomenclature: Dimethyl sulfoxide Methylsulfinylmethane Dimethyl sulfon Methylsulfonylmethane Dimethyl sulfide S-oxide Dimethyl sulfide S,S-dioxide Bonding system of alcohols and ethers Starting point: structure of water - sp3 hybrid state for oxygen (h12h22h31h41) Alcohols – C(sp3)-O(sp3) hetero nuclear -bond Ethers – two C(sp3)-O(sp3) hetero nuclear -bond tetrahedral compound but the bond angle is deformed (R,R1 groups have more space demand) Bond E – both C-O and O-H are strong C-O: 355-380 kJ/mol (compare to: C-C: 345-355 kJ/mol) O-H: 460-465 kJ/mol (compare to: C-H: 400-415 kJ/mol) Bond distance Phenols, phenol ethers, enol ethers: shortening bond distance more stronger bond!! (greater bond order) Reason: interaction between nonbonding e-pair and -e-system (+M effect) Resonance structures: (sp2 hybrid state for oxygen) Seven-center bond with eight electrons - electron delocalization! (parallel PZ orbitals) C-O bond: the increasing double bond character Aromatic ring increased electron density ( OH, OR first order directing groups, activating substituents!) Electron negativities ENC = 2.5, ENO = 3.5, ENH = 2.1 polar hetero nuclear bonds, charge separation permanent dipole moment Tioalcohols and tioethers Formal similarity between O and S BUT in case of sulphur: 3s23p43do (electon cofiguration of oxygen: 1s22s22p4) e. g. or Thiophene (aromatic compound) Further differences: S has larger atom radius (rS = 0.102 nm, rC = 0.077 nm, ro = 0.073 nm) longer and weaker bonds compare to oxygen Non-bonding e-pairs have greater space demand larger deformation compare to oxygen analogues Physical properties of alcohols, ethers and their thio analogous Boiling point, melting point – Typically, higher than alkanes, and alkyl halides, it has homologous series Increasing length of carbon chain makes it closer to R-Cl, RH characteristics (dispersion forces between the alkyl chains become increasingly dominant) Boiling points (oC) Forces R-OH R-SH ~ R-OR1 ~ R-Cl R-H H bond dipole-dipole Induced dipole - Induced dipole H-OH > Me-OH, Et-OH, Pr-OH H-OH > H-SH, R-OH > R-SH worse fit, weakening association weakening H-bond (S nonbonding pair is diffuse) Melting points of n-alcohols (ROH) Melting point: minimum curve – longer alkyl group incorporation into the diamond-like H-bond structure of the ice is not occurs completely so If the alkyl chain is long than „alkane-like” mp can be expected Hydrogen bonding A dipole–dipole attraction between the positively polarized proton of the OH group of one ethanol molecule and the negatively polarized oxygen of another. The term hydrogen bonding is used to describe dipole–dipole attractive forces of this type. The proton involved must be bonded to an electronegative element, usually oxygen or nitrogen. Protons in C―H bonds do not participate in hydrogen bonding. Hydrogen bonding in ethanol involves the oxygen of one molecule and the proton of an ―OH group of another. Hydrogen bonding is much stronger than most other types of dipole–dipole attractive forces. Di- and polyols: highly elevated mp, bp Reason: intermolecular H-bonds, long chains Density: 1 (H2O) – alkyl groups makes the molecule „lighter” Solubility: In Water: H bonds, in low concentrations the solubility is good (n = 1-3: unlimited!) Ethers: worse solubility in water, BUT S(Et2O) = 8 g/100 ml!! „one-sided” H bonds, ether only H acceptor! Thiols: weak H bonds weak solubility in water Preparation of alcohols 1. From alkyl halides by SN reaction Problem: competing elimination (alkene formation) → contaminated product probability R = 1° <2° <3° direction is increasing 2. Hydrolysis of esters The acidic variant an equilibrium reaction, reversal of the esterification. Better: alkaline hydrolysis (≥ 1 equiv base.) Typical: NaOH (KOH)/H2O or NaOH/alcohol, dioxane etc – H2O (solubility!), then H3O A two-step pathway for avoiding elimination SN reaction with a less nucleophile partner, easy ester cleavage Preparation of alcohols 3. Hydration of alkenes (formal or actual water addition) 3.1. Acid-catalyzed addition of water The structure of the major product (regioselectivity) is defined by the Markovnikov’s rule. dilute 3.2. Oxymercuration – demercuration The structure of the major product (regioselectivity) is defined by the Markovnikov’s rule. 3.3. Hydroboration The structure of the major product (regioselectivity) is defined by the Markovnikov’s rule BUT anti-Markovnikov product is formed. 4. Reduction of oxo compounds Opportunities: 1. catalytic reduction (H2/cat., cat. = Pd-C, Pt, PtO2, Raney-Ni, etc.) 2. Metal hydrides (NaBH4/R-OH, LiAlH4/Et2O or THF --- H-) 3. Dissolving metal reduction (Zn/HCl or NaOH, Na/EtOH, etc. --- formation of H2) Preparation of alcohols 5. Reduction of esters In laboratory: LiAlH4 (LAH)/Et2O; Industry: catalytic reduction (harsh conditions, eg. copper-chromite (Cu2Cr2O5)/150-400 oC, 100-300 bar) 6. Reactions of oxo comp. / carboxylic acid derivatives and Grignard reagenst Good news: you already know these reactions Preparation of phenols In laboratory: „cooking” of diazonium salts By-products Diazonium salt Phenol Industry: nowadays starting from cumene The world phenol production: 8.9 million tonnes in 2012. The global phenol foreign trade exceeded USD 3.6 billion in 2012. The world phenol supply is expected to go beyond the 10.7 million tonnes mark in 2016. Preparation of thiols Nucleophilic substitution. Disadvantage: symmetrical ether formation, cause the resultant product is also reactive in nucleophilic reactions so a possible secondary reaction can take place Preparation of thioalcohols 2. A better substituion reaction: Synthesis of thiols through isothiouronium salt The most often used method Preparation of thioethers In a nucleophile substitution reaction Analogy with Williamson’s ether synthesis Thiols and thiophenols reacts readily, Reason: the great nucleophilicity of S (+ easy formation of thiolate, thiophenolate)