Russian Journal of Organic Chemistry, Vol. 38, No. 11, 2002, pp. 1576 1578. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 11, 2002,
pp. 1630 1632.
Original Russian Text Copyright
2002 by Voronkov, Trukhina, Vlasova.
Acyl Iodides in Organic Synthesis: I. Reactions with Alcohols
M. G. Voronkov, A. A. Trukhina, and N. N. Vlasova
Faworsky Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences, Irkutsk, 664033 Russia
Received July 27, 2001
Abstract Reaction of acyl iodides RC(O)I (R = Me, Ph) with alcohols R OH (R = Me, Et, i-Pr, t-Bu,
CH2= CHCH2, HC CCH2) provides in the corresponding organyl iodides R I. Unlike that 2-chloroethanol
and phenol (R = CH2CH2Cl, Ph) react with RC(O)I in the same way as with acyl chlorides yielding esters
RCO2R . This reaction path occurs partially also with methanol and ethanol.
In 1958 Voronkov and Khudobin [1, 2] de-
monstrated that trialkyliodosilanes easily cleave the
bonds C O C, C O Si, and Si O Si. Basing on this
fact 17 years later Voronkov and Dubinskaya were
the first to introduce Me3SiI into organic synthesis
[3] as they reported at two international conferences
[4, 5]. Therewith Me3SiI was shown to readily
produce the rupture of C O C bonds in acyclic and
cyclic ethers. These studies aroused wide interest, and
soon several reviews were published concerning the
application of trimethyliodosilane as iodinating,
deoxygenating, and trimethylsilylating reagent [6, 7].
RC(O)I + R OH
RCO2H + R I
(2)
Similar to reaction with Me3SiI the alkyl iodides
formation is a general process for primary (I, II),
secondary (III), and tertiary (IV) alcohols, and also
for unsaturated alcohol both with a double (compound
V) and a triple (compound VI) bond. The reaction of
RCOI with these alcohols at equimolar ratio and
60 100 C is completed within 1.5 2 h. The yield of
alkyl iodides does not change at excess RCOI. No
liberation of hydrogen iodide occurred in this process
as indicated the absence of products of HI addition to
the double bond of the allyl alcohol.
We attempted to develop alternative or equivalent
to the trimethyliodosilane deoxigenating and iodinat-
ing agents that would provide new opportunities in
organic and organoelemental synthesis. As such we
selected acyl iodides RCOI, in particular, their
simplest representatives (R = Me, Ph). These are
easily obtained by treating the corresponding acyl
chlorides with sodium iodide [8]. It should be noted
therewith that acyl iodides are poorly studied com-
pounds, and even in the book [9] dedicated specially
to acyl halides there are only few citations regarding
the acyl iodides. Starting the studies in this field we
carried out reactions of acyl iodides with aliphatic
alcohols R OH [R = MenCH3 n, n = 0 (I), 1 (II),
2 (III), 3 (IV); CH2= CHCH2 (V); HC CCH2 (VI);
ClCH2CH2 (VII)], and phenol VIII. The trimethyl-
iodosilane reacts with alcohols as a iodinating agent,
and this reaction was proposed for synthesis of
organyl iodides [10]. Acyl chlorides RCOCl were
long ago established to afford with alcohols the cor-
responding esters RCOOR [9, 11] [Scheme (1)].
Unlike alcohols I VI 2-chloroethanol (VII) and
phenol (VIII) with RCOI yield the corresponding
esters and not organyl iodides [Scheme (3)].
RC(O)I + R OH
RCO2R
+
HI
(3)
Reaction (3) partially occurred alongside reaction
(2) also with methanol and ethanol. As a result alkyl
iodides R I (R = Me, Et) and esters RCO2R formed
in 1: 1 weight ratio. With excess RC(O)I the yield of
R I increased and that of RCO2R respectively
decreased.
Reaction (3) occurred apparently due to the
relatively high acidity of the hydroxy group of
2-chloroethanol (VII) and phenol VIII and to some
extent of methanol (I) and ethanol (II). It is seen from
the acidity constants pKa of the alcohols I IV under
study which amount to 15.1, 15.9, 18.0, and over
19.0 respectively. Therewith the pKa values for
2-chloroethanol and phenol are respectively 11.2 and
9.9. Thus the acidity of the alcohol switches the
mechanism of its reaction with acyl iodides. For
instance, the reaction of acyl iodides with the alcohols
of low acidity I IV results in substitution of the
hydroxy group with the iodine atom. The process
RC(O)Cl + R OH
RCO2R
+
HCl
(1)
In contrast the acyl iodides under study reacted
with aliphatic alcohols similarly to trimethyliodo-
silane [Scheme (2)].
1070-4280/02/3811-1576$27.00 2002 MAIK Nauka/Interperiodica