Dẫn xuất halogen

HOÁ HỌC HỮU CƠ
Organic Chemistry
CHƯƠNG 9 (T.T)
DẪN XUẤT HALOGEN & HC CƠ-Mg
Hợp chất cơ kim
Organometallic Compounds
Danh pháp
Organometallic Nomenclature
Metal is the parent
Carbon-Metal Bonds
in
Organometallic Compounds
F 4.0 H 2.1
O 3.5 Cu 1.9
N 3.0 Zn 1.6
C 2.5 Al 1.5
H 2.1 Mg 1.2
Li 1.0
Na 0.9
K 0.8
Table 14.1 (p 588)
Polarity of Bonds
+
–
–
+
organometallics are a source of nucleophilic carbon
Polarity of Bonds
CH3F
CH3Li
Preparation of Organolithium Compounds
same for Ar—X
is an oxidation-reduction reaction: carbon
is reduced

Organolithium Compounds
normally prepared by reaction of alkyl halides
with lithium
Examples
(CH3)3CCl + 2Li
diethyl
ether
–10°C
(CH3)3CLi + LiCl
(75%)
Br
+ 2Li
diethyl
ether
35°C
Li
+ LiBr
(95-99%)
Electron Bookkeeping
+ Li+
•
–
•
Preparation of
Organomagnesium Compounds:
Grignard Reagents
same for Ar—X
Grignard Reagents
RMgX
prepared by reaction of alkyl halides
with magnesium
Diethyl ether is most often used solvent. Tetrahydrofuran is also used.
Examples
diethyl
ether
–10°C
(96%)
Br
+ Mg
diethyl
ether
35°C
MgBr
(95%)
+ Mg
Electron Bookkeeping
+ Mg+
•
–
•
•
•
I > Br > Cl >> F
RX > ArX
Order of Reactivity
certain groups cannot be present in
the solvent
the halide from which the Grignard reagent
is prepared
the substance with which the Grignard
reagent reacts
Forbidden Groups
Anything with an OH, SH, or NH group
Forbidden Groups
therefore cannot use H2O, CH3OH, CH3CH2OH, etc. as solvents
cannot prepare Grignard reagent from substances such as HOCH2CH2Br, etc.
Organolithium and Organomagnesium Compounds as Brønsted Bases
Brønsted basicity
••
•
•
–
+
Grignard reagents (M = MgX) and organolithium reagents (M = Li) are strong bases.
Example
(100%)
+ H2O
+
LiOH
CH3CH2CH2CH2Li
CH3CH2CH2CH3
Example
MgBr
(100%)
+ CH3OH
+
CH3OMgBr
Table 14.2
Approximate Acidities
Compound pKa
(CH3)3CH 71
CH3CH3 62
CH4 60
Ethylene 45
Benzene 43
Ammonia 36
Acetylene 26
Water 16
Hydrocarbons are very weak acids.
Their conjugate bases are very strong bases.
Grignard reagents and organolithium reagents are strong bases.
Acetylenic Grignard Reagents
are prepared by an acid-base reaction
CH3CH2MgBr
+
CH3CH3
+
Alkyl halides in Nature
Aplysamine from Psammaplysilla purpurea
Cytotoxic