hydroxy derivatives of hydrocarbons (alcohols, phenols
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Hydroxy derivatives of hydrocarbons (alcohols,
phenols, ethers) and sulfur analogues:
Bonding system characterization. Physical properties. Acid-
base 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:
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!
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
n 1
Formally - a water/a hydrogen sulphide is
substituted with hydrocarbon radicals
BUT! for sulphur empty d orbitals, S = O bond is
formed ("four and six valence" sulphur!)
1-C-OH bonded compounds (alcohols, phenols, enols)
ethanol phenol vinyl alcohol
NomenclatureFunctional class nomenclature
Functional class names of alcohols are derived by naming the alkyl group that bears the hydroxylsubstituent (-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 nomenclatureSubstitutive names of alcohols are developed by identifying the longest continuous chain that bears the hydroxyl group and replacing the -e ending of the (pentane) 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 reflecttheir 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) - Enol ethers: specific, different (higher) reactivity [-C = C-OR (Ar)]
Special types of ether
3. C-O-O-H, C-O-O-R compounds
Formally, the alkylated / arylated derivatives of hydrogen peroxide
Cyclic ethers epoxides (oxiranes) hemiacetal acetal orthoester
special compounds: different reactivity than
cyclic ether
Similarity to aldehydes and ketones
Relation to carboxylic acids
Ether derivatives of geminal diols
Nomenclature of ethers
Ethers are named, in substitutive IUPAC nomenclature, as alkoxy derivatives of alkanes.ONLY alkoxy / aryloxy prefix + base carbon chain
Substitutive 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 twogroups bonded to oxygen are the same or different. Unsymmetrical ethers are also calledmixed ethers. Diethyl ether is a symmetrical ether; ethyl methyl ether is an unsymmetrical ether.
Functional class IUPAC nomenclature
Cyclic ethers have their oxygen as part of a ring—they are heterocyclic compoundsSeveral have specific IUPAC names.
trivial names, additive nomenclature, Hantzsch-Widman nomenclature
(additive nomenclature)
Hantzsch-Widman 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.
Nomenclature of ethers 2.
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, arenthiols, thioethers
Derivatives with more than two ligands
Relationship with sulfones according to the
binding system, chemically similar to
carboxylic acids
thioalcohol arenthiol sulfide (thioether) disulfide if n>2 polysulfideR1=R2 or R1≠R2 different from oxygen
sulfinyl group sulfonyl group
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.
Nomenclature of thiols
Substitutive IUPAC names
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 olderliterature.
aromatics: benzenethiol nomenclature (in the older literature thiophenol name is used)
Hydroxyl groups take precedence
over sulphanyl/mercapto group.
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
Substitutive nomenclature of sulfides
Functional class IUPAC names of sulfidesFunctional 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 six-membered rings are named thiirane, thietane, thiolane, and thiane, respectively.
Nomenclature of sulfides
Substitutive nomenclature:
Functional class IUPAC names:
Substitutive nomenclature
prefix: alkylsulfinyl, arylsulfinyl, alkylsulfonyl, arylsulfonyl
Nomenclature of sulfoxides and sulfones
Functional class nomenclature
hydrocarbon group names + sulfoxide / sulfone suffix
Additionally: Compound Name + S-oxide / S, S-dioxide suffix
Dimethyl sulfoxideMethylsulfinylmethane
Functional class nomenclature:Substitutive nomenclature:
Dimethyl sulfonMethylsulfonylmethane
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 (h12h2
2h31h4
1)
Alcohols – C(sp3)-O(sp3) hetero nuclear -bondEthers – 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 strongC-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)
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)
Seven-center bond with eight electrons - electron delocalization!
(parallel PZ orbitals)
Resonance structures:
C-O bond: the increasing double bond character Aromatic ring increased electron density ( OH, OR first order directing groups, activating substituents!)
Bond distance
(sp2 hybrid state
for oxygen)
Electronegativities
ENC = 2.5, ENO = 3.5, ENH = 2.1 polar hetero nuclear bonds, charge separation permanent dipole moment
Tioalcohols and tioethersFormal similarity between O and S BUT in case of sulphur: 3s23p43do
(electon cofiguration of oxygen: 1s22s22p4)
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
or
e. g.
Thiophene (aromatic compound)
Physical properties of alcohols, ethers and their thio analogousBoiling point, melting point – Typically, higher than alkanes, and alkyl halides, it has homologous seriesIncreasing length of carbon chain makes it closer to R-Cl, RH characteristics (dispersion forces between the alkyl chains become increasingly dominant)
R-OH R-SH ~ R-OR1 ~ R-Cl R-H
Forces H bond dipole-dipole Induced dipole - Induced dipole
H-OH > Me-OH, Et-OH, Pr-OH worse fit, weakening associationH-OH > H-SH, R-OH > R-SH weakening H-bond (S nonbonding pair is diffuse)
Boiling points (oC)
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 soIf the alkyl chain is long than „alkane-like” mp can be expected
A dipole–dipole attraction between the positively polarized proton of the OH group ofone ethanol molecule and the negatively polarized oxygen of another. The termhydrogen 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
Hydrogen bonding in ethanolinvolves the oxygen of one molecule and the proton of an ―OH group of another. Hydrogen bonding is muchstronger than most other types of dipole–dipole attractiveforces.
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 reactionProblem: competing elimination (alkene formation) →contaminated product probability R = 1° <2° <3°direction is increasing
2. Hydrolysis of esters
The acidic variant is 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 alcohols3. 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.
3.2. Oxymercuration – demercuration
3.3. Hydroboration
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)
The structure of the major product (regioselectivity) is defined by the Markovnikov’s rule.
The structure of the major product (regioselectivity) is defined by the Markovnikov’s
rule BUT anti-Markovnikov product is formed.
dilute
Preparation of alcohols
5. Reduction of esters
In laboratory: LiAlH4 (LAH)/Et2O;
Industry: catalytic reduction (harshconditions, eg. copper-chromite
(Cu2Cr2O5)/150-400 oC, 100-300 bar)
6. Reactions of oxo comp. / carboxylic acid derivatives and Grignard reagenst
Do you know these reactions ????
Preparation of phenolsIn 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 tradeexceeded USD 3.6 billion in 2012.The world phenol supply is expectedto go beyond the 10.7 million tonnesmark in 2016.
Preparation of ethers
LG = Hlg, OSO2Q, OSO2OR1
Ethers can be synthesized from alcohols or phenols by nucleophylic substitution – This is
Williamson-type ether synthesis
The structure of methylating agents
Alkylating agents:
- Alkyl halide
- Sulphonic acid esters
- Dialkyl sulphates
Some problems:
First:
Second:
Preparation of thiols
Nucleophilic substitution. Disadvantage: symmetrical thioether formation, cause the resultant product is also reactive in nucleophilic reactions so a possible secondaryreaction can take place
A better substitution reaction:
Synthesis of thiols through isothiouronium salt
The most often used method
thiourea
Oxymercuration – demercuration: synthesis of ethers by electrophillic addition of alcohols
The structure of the major product (regioselectivity) is defined by the Markovnikov’s rule.
Preparation of thioethers
In a nucleophilic substitution reaction
Analogy with Williamson’s ether synthesis
Thiols and thiophenols reacts readily,
Reason: the great nucleophilicity of S (+ easy formation of thiolate, thiophenolate)
thiolate thiophenolate
Same problems as in the case of ethers:
First:
Second:
Preparation of benzene thiols (thiophenols)
It can be synthesized from arylsulfonyl chloride by simple reduction or by the reaction of
Grignard reagents with elemental sulphur.
It can be prepared from phenols too, in a three-steps procedure. First, the phenol was
reacted with N,N-dialkyl-tiocarbamoyl-chloride, followed by the Pd catalyzed
rearrangement and hydrolysis .
Chemical properties of alcohols, ethers and thio analogues
Starting point: polar compound, heteroatoms electron excess (greater e- density), H loses e-
Sulphur: polarisable!
1.1. Basicity: non-bonding e-pair/partial negative charge Brönsted base, Lewis base
e. g. BF3Et2O bp: 127 oC, it
can be distilled!
1. Acid-base properties
2.1. Acidity - alcohols (phenols, enols), thiols: strongly polarized H-O bond (requirement for acidity) possible deprotonation, Brönsted acidity
The required base deprotonation strength depends on the acidity of RX-H compound. Acidity depend on the stability of the formed anion during the deprotonation!!
Tendencies:✓ R-OH ~ H2O, depending on the order of alcohols: 1o > 2o > 3o
✓ Ar-OH > R-OH✓ R-SH > R-OH
B: metal or
Acidity of alcohols, phenols Acidity of substituted phenols
deprotonation
Picric acid
Explanation of tendencies of acidity – stability of anions
Phenols: charge delocalisation on the aromatic system (after the deprotonation of phenols)
Phenolate: LCAO-MO: 7 centred bond with 8 electrons greater Ka than alcohols
Resonance structures
G‡
R-OH + B:
Ar-OH + B:
R-O: + HB
Ar-O: + HB
Thiols: After the deprotonation the pairs of electrons distributed in bigger space (cf. larger ion radius of sulphur)
MeO: MeS:
Phenolate anion
Reactions can be derived directly from the bonding system - the nucleophilic character
Differences between alcohols and phenolsPhenols: stronger C-O bond O-H bond cleavage is preferred (weaker bond + the stability of phenolate ion) acid catalysed process (C-O bond cleavage) are rare!
C-O bond cleavage:Initiating step: protonation under
acidic condition
O-H bond cleavage:Initiating step: deprotonation under
neutral or basic condition
Chemical properties of alcohols1. Ether formation
LG = Hlg, OSO2Q, OSO2OR1
e.g. methylating agents
Notes: aryl halides (except if it is actyvated) no reaction alcoholate is better nucleophile strong base necessary for preparing an alcoholate
phenols have greater acidity even aqueous basic solution can used (NaOH, KOH, Na2CO3/H2O)
1.2. Ether synthesis with solvolysisSolvolysis: itself the solvent is the nucleophile
1.3. Ether synthesis under acidic condition (acid catalysed nucleophile substitution)
Importance: the most applied ether synthesis
Acidic activation, alcohol has double role.
Formally: intermolecular water elimination
Synthetic importance: symmetrical ethers
Nucleophile substitution (O-nucleophile!)
1.1. Williamson’s synthesis (R1 = alkyl, allyl, benzyl)
Acid catalysed ether synthesis - mechanism: carbocation intermediate
BUT! Competitive reaction with elimination: alkene formation ( elimination)
tendency!
Alkene formation: Zaitsev’s rule (more stable alkene is formed)
Chemical properties of alcohols
Ether formation is favoured if: 1o or 2o alcohol large ROH concentration cat. amount H
lower temperature
2. Ester formation
General:
Esters of inorganic acids
Carboxylic acid esters
Acid catalysed acylation (3 mechanism)Equilibrium!!
In practice an important step: acylation
Most important acylating agents:
Important biological role: DNA, RNA: nucleotide, nucleic acid (Organic chemistry III.)
Chemical properties of alcohols
Phosphoric acid esters
Trialkyl phosphate
AdN + E mechanism
NO Equilibrium!!!
Sulfonate ester derivatives:
Importance: sulfonate esters are good leaving groups (as sulfonate anion: R1SO2O: ), SN
reactions!! To replace OH group with other substituent: first transform OH to sulfonateester then do the substitutive reaction
Hydrogen halides: alkyl halides
Acid catalysed SN, waterelimination!
General condition: cc. HHlg/Δ. In case of 3o alcohols even at room temperature
Chemical properties of alcohols
OH group badleaving group
The oxidation states above alcohol levels: aldehyde / ketone; acid possible oxidation products. The structure of the product and the required conditions (reactivity) depends on the structure of the starting alcohol.
RCHO easy oxidizability ; partial oxidation requires special reagents and conditions: Cr (VI), or removal of aldehyde
Industry: catalysts for dehydrogenation (CuO-Cu/300 oC). Important reaction: EtOH → MeCHO
2. 2o Alcohols
Chemical properties of alcohols - OXIDATION
Mixture of carboxylic acids
harsh oxidation
Up to ketone the oxidation takes place readily
Oxidizing agents: CrO3/H2SO4 (Jones reagent), CrO3*2Py/DCM (Collins reagent), K2Cr2O7/H2OCr(VI) (orange)→ Cr(III) (green)
BUT, KMnO4/H+ or KMnO4/H2O chain cleavage
Cr(VI)
1. 1o Alcohols
3. 3o Alcohols
Difference: there is no opportunity for dehydrogenation in alkaline or neutral medium, no reaction.
BUT! In acidic medium: first dehydratation then alkene chain cleavage
Note: the biological oxidation of alcohols is also possible.
For example: The oxidation of ethanol to acetaldehyde with the help of dehydrogenase enzyme
Chemical properties of alcohols - OXIDATION
Chemical properties of phenols
Easy deprotonation – potential O-nucleophile acylation (ester formation) sulfonylation (sulfonate ester formation) alkylation (ether formation)
Oxidation of phenols – takes place easily
Phenol
OH groups with acidic H can be alkylated with
diazoalkanes
Alkylation:ethers Acylation:
esters
Sulfonylation: sulfonate ester
or
During storage it gets coloured since the OH group has high +M effectthat results large e-density in the aromatic ringoxidation is easy1,2-(OH)2 and 1,4-(OH)2 benzenes
1,2-benzoquinone 1,4-benzoquinone
Aromatic electrophilic substitution of phenols – the OH group will not react but it has directing effect
Use of salicylic acid: production of Aspirin®
Chemical properties of phenols
Kolbe reaction: electrophile: O=C=O
effect
Highly activated and very reactive aromatic ring
picric acid
The reaction occurs in aqueous solution without
a catalyst!!!Polyhalogenation
Dilute HNO3
phenol
willow bark ( natural source of salicylic acid) can ease pain and reduce fevers
Phenol-formaldehyde resins
Crosslinkedpolycondensationplastic: bakelite
Baekeland (inventor)
Chemical properties of phenolsHydroxy-methylation
Importance
C-O-C highly polarized but strong bond
Based on binding system may be a direct SN reaction... But! Alkoxy group is a bad leaving group because the weak stabilization no bond cleavage
Consequence:Ethers are slightly reactive, no reaction in neutral and basic medium, inert to the alkali and alkaline earth metals, organometallic compounds and dilute (!) acids
Ideal solvents (e.g. Grignard reaction), extraction agents
Possible reactions: based on Brönsted / Lewis basicity: protonation, coordination Lewis acids (for ACTIVATION ...)
Activation: Protonation - strong acids, strong acidic conditions
Question: what is the nucleophile ?? A typical solution is concentrated HHlg / Δ
Because of the secondary reaction -- small synthetic application: mixture of alkyl halides...BUT! For phenol ethers selective cleavage of due to the different binding energies of C-O.Furthermore, there is no secondary reaction due to the strong Ar-O bond. (Protective Group!!!)
Chemical properties of ethers
Good leaving group
Cleavage of acetals, enol ethers - much easier than "simple" ethers - with dilute acidic medium
Reversible equilibrium reaction - the same mechanism in both directions. Reverse direction: Synthesis of acetals from oxo compounds
Reaction of epoxides
Chemical properties of ethers
Typical reaction: ring opening preparation of 1,2-disubstituted systems (alcohols)
Three-membered strained ring:• Large Bayer – strain (Angle strain, The 60o bond angles are much smaller
than the optimum 109.5 o angles of a normal tetrahedral carbon atom)• Large Pitzer - strain (eclipsed groups) → high reactivity
Nu attack
protonation
more stable tautomer(constitutional isomer)
Baeyer suggested that three- and four-membered rings suffer from what we now callangle strain. Angle strain is the strain a molecule has because one or more of its bondangles deviate from the ideal value; in the case of alkanes the ideal value is 109.5°.
Angle strain: destabilization that results from distortion of bond angles from theirnormal values
Torsional strain: destabilization that results from the eclipsing of bonds on adjacentatoms
Chemical properties of ethers - ring-opening of epoxides
Ring opening in neutral or alkaline medium - nucleophile attack of the epoxy carbon atoms.An ether functional group substitution by nucleophile, different reactivity than simple ethers due to the ring strain!
Ring opening in acidic medium - nucleophile attack on the epoxy protonated carbons
O-nucleophile → C-O bond
N-nucleophile → C-N bond
C-nucleophile→ C-C bond
Antiperiplanar (trans) OH and Nu
Solvents, paint and varnish industry
Ethylene glycolbond
Ethylene glycol
monoethyl ether
Chemical properties of ethers - Oligo-and polyethylene glycols, crown ethers
Diethylene glycol Triethylene glycol
Good solvatation of cations
High boiling point, good solventsReactions with metal salts at high T
Cyclic derivatives: crown ethers
12-crown-4 18-crown-6 15-crown-5
Complex formation according to the size of metal salts Li+ --- 12-crown-4 Na+ --- 15-crown-5 K+ --- 18-crown-6
Use:➢ Crown ethers are used in the laboratory as phase transfer catalysts➢ Medical use: remove metal ions from living body
Ethylene oxide as starting material
Polyethylene glycol
In chemistry, a phase-transfer catalyst or PTC is a catalyst that facilitates the migrationof a reactant from one phase into another phase where reaction occurs. Phase-transfercatalysis is a special form of heterogeneous catalysis.Ionic reactants are often soluble in an aqueous phase but insoluble in an organic phasein the absence of the phase-transfer catalyst. The catalyst functions like a detergent forsolubilizing the salts into the organic phase.Phase-transfer catalysis refers to the acceleration of the reaction upon the addition ofthe phase-transfer catalyst. By using a PTC process, one can achieve faster reactions,obtain higher conversions or yields, make fewer byproducts, eliminate the need forexpensive or dangerous solvents that will dissolve all the reactants in one phase,eliminate the need for expensive raw materials and/or minimize waste problems.Phase-transfer catalysts are especially useful in green chemistry—by allowing the use ofwater, the need for organic solvents is reduced.
Chemical properties of thiols and thioethers
Chemical properties of thiols - starting point: considerable acidity, RS: easy generation
RS: excellent nucleophilethiols readily can be acylated, alkylated, etc.. - The similarity to alcohol!
Difference: oxidation reactions (compared to alcohol - more possibility)
Reaction with Csp3 electrophiles
Reaction with Csp2 electrophiles
Acid cat. AdNC=O
Acyl SN (AdN+ E)
Mild oxidation or or weak base (in cat. amount)
Harsh oxidation
Significance of sulfonic acids:Detergents, pharmaceutical
Oxidizing agents:
Biological importance:
thioether
thioester
thioacetal
disulfide
sulfonic acid
Alkylation – S as nucleophile
Oxidation - Preparation of sulfoxides, sulfones with electrophilic oxidizing agents
Chemical properties of thiols and thioethers
Chemical properties of thioethers
Sulfonium salts
Stable, solid compoundscan be chiral if R =R1=R2
Oxidizing agents:
difficult
Prep. of sulfoxides with oxidation is not easy:• Requires mild reaction conditions (0-25 oC)• 1 equiv. oxidizing agents
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