A powerful tool for acid catalyzed organic addition and substitution reactions

Article abstract of DOI:10.1039/c4ra17321j

A novel green chemistry tool for acid catalyzed reactions has been developed. The multipurpose tool is based on the ability of dry solid materials to donate protons (H⁺) to starting materials combined with the simultaneous use of a nucleophile (e.g. NaI). The methods enable the following reactions to be conducted at 20-50 °C: selective addition of iodine or alcohols to more substituted carbon in R₂CCH₂ systems (R ≠ H), esterification reactions, e.g. free fatty acids with methanol, and at higher temperatures, (60-100 °C): esterification of free fatty acids with hindered alcohols (isopropanol), addition of iodine to CC bonds, opening of oxygen(s) containing heterocyclic rings, selective substitution of primary OH groups to iodine in the presence of other functional groups or secondary alcohol groups, esterification of alcohols with nitriles (R-CN), transesterification of fatty acid triglycerides to biodiesel and selective derivatization of primary hydroxyl groups (-CH₂OH) over secondary moieties of sugars without any protection. Most of the reactions were also performed by a re-used Dowex cation exchange resin.

Full text of DOI:10.1039/c4ra17321j

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A powerful tool for acid catalyzed organic addition
and substitution reactions†
Cite this: RSC Adv., 2015, 5, 26218
Petri A. Turhanen* and Jouko J. Vepsalainen
¨
¨
A novel green chemistry tool for acid catalyzed reactions has been developed. The multipurpose tool is based
+
on the ability of dry solid materials to donate protons (H ) to starting materials combined with the simultaneous
ꢀ
use of a nucleophile (e.g. NaI). The methods enable the following reactions to be conducted at 20–50 C:
selective addition of iodine or alcohols to more substituted carbon in R
2
C]CH
2
systems (R s H),
ꢀ
esterification reactions, e.g. free fatty acids with methanol, and at higher temperatures, (60–100 C):
esterification of free fatty acids with hindered alcohols (isopropanol), addition of iodine to C^C bonds,
opening of oxygen(s) containing heterocyclic rings, selective substitution of primary OH groups to iodine
in the presence of other functional groups or secondary alcohol groups, esterification of alcohols with
nitriles (R–CN), transesterification of fatty acid triglycerides to biodiesel and selective derivatization of
Received 31st December 2014
Accepted 4th March 2015
DOI: 10.1039/c4ra17321j
2
primary hydroxyl groups (–CH OH) over secondary moieties of sugars without any protection. Most of
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the reactions were also performed by a re-used Dowex® cation exchange resin.
Surprisingly, although solid ion exchange resins have been
available for a more than a hundred years, there are no
Introduction
1
Today there is an increasing demand for green chemistry previous publications in the literature on this specic use. The
methods and technologies in industrial processes, to reduce system developed here resembles in someways those conducted
2
waste and to eliminate the use and generation of hazardous with ionic liquids, e.g. acetylation of alcohols with acetonitrile,
substances. Here we describe a novel multipurpose tool to although isolation of the product is more straightforward in the
selectively perform organic addition and substitution reactions best case requiring only ltration and solvent evaporation for
in solutions based on dry solid materials, which are recyclable, the product to be ready for the next step.
acutely non-toxic and easy to handle. This novel system enables
acid-catalyzed organic reactions without involving special
reaction conditions or complex separation steps, enabling Results and discussion
synthesis of compounds that are difficult or even impossible to
prepare by other currently known methods. Typical examples of
This reaction system was initially discovered by chance when we
were trying to develop novel synthesis strategies for prepairing
these reactions include esterication reactions at room
ApppI, the isopentenyl derivative of ATP, which is one of the key
temperature with quantitative yields, opening of six membered
metabolic compounds formed when cells are treated with
oxygen-containing heterocyclic rings to produce haloalkanols,
selective substitution of the primary HO-group to nucleophiles
3
nitrogen containing bisphosphonates. The unexpected reac-
tion was found when attempts were made to prepare the ApppI
in the presence of other types of HO-groups and addition of
intermediate 2b under rather standard conditions as shown in
iodine to multiple bonds using alkali metal iodide (e.g. NaI) as
Scheme 1. In this approach, sodium iodide was used as the
an iodine source.
4
demethylation agent to prepare compound 2a from dimethyl
The tool developed here, is based on the ability of dry solid
+
derivative 1 followed by addition of the H form Dowex® resin to
materials, such as Dowex® resin or solid bisphosphonates, to
+
exchange the sodium for a proton. Unexpectedly, aer solvent
evaporation, the residue contained mixture of two
compounds, not only 2b as expected, but, based on H, C,
donate protons (H ) to starting materials combined with the
a
simultaneous use of a salt form nucleophile (e.g. NaI), which
acts either as a catalyst, as in the esterication reactions, or as a
reagent, e.g. in the addition of iodine to multiple bonds.
1
13
31
P
NMR and mass spectrometry data, the second product was
veried as compound 3a. We speculated that the reaction had
been made possible due to the presence of trace amounts of NaI
University of Eastern Finland, School of Pharmacy, Biocenter Kuopio, P.O. Box 1627,
+
among compound 2a when H Dowex® was added. In the
FIN-70211, Kuopio, Finland. E-mail: petri.turhanen@uef.
literature, similar selective addition reactions of HI to terminal
†
Electronic supplementary information (ESI) available: Detailed experimental
5
H
2
C]CR
2
(R s H) bonds are extremely rare while addition of
procedures and NMR characterization data for all prepared compounds. See
DOI: 10.1039/c4ra17321j
iodine to other kinds of double bonds are rather common.
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Scheme 1 Discovery of the unexpected reaction.
Aer a systematic study of this reaction, we noticed that the unknown. Unexpectedly, by using the novel tool reported here,
key to the reaction was the oven-dried solid material containing (E)-2,3-di-iodo-prop-2-en-1-ol (11) could be prepared in the dark
–
3 2 3 2
SO H, –CO H and/or –PO H groups as a part of material from propargyl alcohol (10) using dry NaI as an iodine source
structure mixed with the dry salt form nucleophile in a protic or and achieving a 60% yield. The absolute structure has been
polar aprotic solvent. Typically, solid materials containing the veried by X-ray crystallography and will be reported elsewhere.
above mentioned groups are strong cation exchange resins,
The ring-opening reactions of a saturated heterocyclic ring
such as Dowex® and Amberlyst® type materials, but the addi- containing ether bonds depend on the ring size, since small
tion of HI to terminal H C]CR (R s H) bonds was also strained rings such as oxirane and oxetane are rather easily
2
2
successful when conducted with solid microporous opened under acidic conditions. In addition, hundreds of
6
bisphosphonates. In the case of nucleophiles, sodium iodide literature references are available describing the preparation
was typically used in the reactions to achieve the best yields. In of 5-halopentanol from tetrahydrofurane (THF), but there are
+
+
+
+
+
2+
3+
addition, other X I
n
(X ¼ K , Rb , Ni , NH , Mn , Sb , n ¼ 1, 2 only a couple of reports in which 6-halohexanol has been
4
or 3) salts were tested in the esterication of oleic acid with prepared directly from tetrahydro-2H-pyran (THP), and only
MeOH, but lower and variable yields were obtained. Addition of one of them actually describes the synthesis of 6-iodohexanol
7
bromine to the H C]CR (R s H) bond using NaBr as a (13a) from THP using NaI and toxic BF -etherate. The reaction
2
2
3
bromine source was also successful (reactions with bromides opening 1,4-dioxane to 2-(2-iodo-ethoxy)-ethanol (13b) has not
using the system reported here are being studied more previously been described. Actually, none of the above
+
ꢁ
ꢁ
ꢁ
ꢁ
systemically and will be reported in the near future), but chlo- mentioned ring-opening reactions with X Y (Y ¼ Br or I )
ride did not react even at elevated temperatures. Aer realizing salts over activated acidic solid supports have been reported
that the addition reaction mentioned above was based on a previously.
novel reaction strategy to prepare acid catalyzed reactions, we
started to systematically map and determine which other hydroxyl group with any kind of alkyl chain by a halogen (Cl ,
transformations would be possible under similar conditions. Br or I ) moiety is a highly unfavourable process, since the OH
Direct substitution of a primary, secondary or tertiary
ꢁ
ꢁ
ꢁ
We have so far tested about 50 different reaction types with the group is a poor leaving group due to its high pK value. Typically
a
most representative examples of the successful ones compiled this substitution reaction (OH to halide) is achieved by using a
in Table 1.
The above described addition reaction was selective for iso- the hydroxyl group to a better leaving group e.g. via tosyl addi-
lated H C]CR (R s H) bond systems at room temperature tion and then changing it to halide. Until now, there have been
large excess of halide as the starting reagent or by rst changing
2
2
1
and according to the H NMR spectral data, quantitative no reports of direct OH substitution to iodine under the present
conversions could be achieved although isolated yields were conditions. As an example, octyl iodide (15a) was prepared from
lower. It was even possible to prepare monodeuterated octanol (14a) using 2 eq of dried NaI and 12-iodo-dodecanoic
compound 5b when the sodium form of Dowex® resin was acid (15b) from 12-hydroxy-dodecanoic acid (14b) using 2.15
treated with DCl/D
2
O and the reaction was performed in eq of dried NaI with 43% and 71% isolated yields, respectively.
8
CD OD. Addition reactions of iodine to other types of mono-, di- For comparison, when the highly reactive ZrCl /NaI system is
3
4
and trisubstituted double bond systems were tested in prelim- used as a reagent for octyl iodide (15a) preparation from octanol
inary experiments but resulted in either mixtures of products or (14a), excellent 97% yield has been achieved. This is a much
unreactive starting materials. However, it also seems possible to greater yield than with our reported method, but conversely,
add iodine to other kinds of double bond systems at elevated there are no reports in the literature of any method for single-
temperatures, although this will need to be examined more step preparation of u-iodo-alkanoic acids from u-hydroxy-
systematically. In the case of carvone (6), it was possible to alkanoic acids.
ꢀ
isolate the iodine adduct 7 aer a 2 h reaction time at 20 C, but
From the scientic point of view, the above-mentioned
the aromatic carvacrol (9) was the main product formed with reactions are considered benecial and advantageous
longer reaction times (>10 h). Moreover, in the presence of producing various end products, starting materials and inter-
ꢀ
alcohols as solvents at elevated temperatures (>40 C), ethers 8 mediates e.g. for medicinal chemistry purposes. However, if one
were obtained, probably either via direct addition of alcohols to considers the procedure in terms applications to green chem-
the terminal double bond and/or via substitution of iodide from istry, one of the key reactions in our system is esterication of
intermediate 5a.
In general, addition of iodine to a triple bond is a known acids in methanol at room temperature achieve quantitative
reaction, but typically the iodine has originated from I . One-pot yields to the corresponding methyl esters, which are the main
acids with alcohols. In particular, esterication of free fatty
2
ꢁ
+
reactions, in which iodide has originated from X I salts are components of biodiesel.
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Table 1 Overview of the reactions
a
a
Conditions
yield
Conditions
yield
b
b
Substrate
Product
Substrate
Product
r.t. 10–15 min.
r.t. 2 h
6
5
5% (5a)
4% (5b)
45%
ꢀ
4
0–50 C,
r.t.,
overnight
overnight
1% (8a)
5% (8b)
4
6
5
4
89%
Reux,
overnight
ꢀ
6
6
5 C, overnight
68% (13a)
33% (13b)
30% (13c)
0%
ꢀ
8
5–100 C, 5 h
to overnight
r.t., 15 min–1
4
7
3% (15a)
1% (15b)
h 99%
ꢀ
8
5–100 C,
overnight
ꢀ
1
4b
85 C, 4 h 70%
14a
40% (19a)
1% (19b)
4
ꢀ
6
8 C,
ꢀ
5
0 C, 2 h (100%
overnight
approx.
0%
conversion)
4%
6
c
9
ꢀ
8
5 C,
ꢀ
1
5
15 C, overnight
6%
overnight
3%
8
a
In the table only the reaction time and temperature has been highlighted, detailed experimental procedures and conditions can be found in the
+
+
supporting info; Dowex® H (D for 5b) ion exchange resin was used in all reactions reported in this table, some of the reactions can be performed
+
also using either 11-amino-1-hydroxyundecane-1,1-diylbisphosphonic acid, Diphonix® or Amberlyst® H ion exchange resin instead of Dowex®
b
c
Isolated yields. It was impossible to measure the exact yield because the real fatty acid composition of 22 was not known, r.t. ¼ room
temperature, oven dried NaI was used in all reactions.
There are several methods for direct esterication of fatty yield is 88%) and product isolation is more complicated when
acids to the corresponding esters by alcohols based on both compared with the method described here. It is possible to
9
10
homogenous catalysis, such as p-TosOH or H
2
SO
and heterogeneous catalysis: sulphated ZrO –TiO
montmorillonite, and 12-tungstophosphoric acid anchored to diazomethane
4
catalysis or perform quantitative esterication of fatty acids to their methyl
11
12
ꢀ
esters at 20 C with highly reactive esterication agents, such as
2
I ,
2
2
systems,
13
16
17
or PPh –I
3 2
reagent.
The closest results
14
SBA-15, have been developed but all these methods require compared to the method described here have been obtained with
elevated temperatures (40 C – 100 C) and long reaction times (4 cerium(IV) ammonium nitrate reagent with a 2 h reaction time
h–48 h). One can conduct esterication at room temperature with and 99% yield, but product isolation is more complex.
ꢀ
ꢀ
18
15
ionic liquid, but the typical reaction times are 3–5 h, the yields
The mildest reaction conditions with which to obtain the
of fatty acid esters are lower (e.g. oleic acid methyl ester, reported quantitative esterication of oleic acid (16) to its methyl ester
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(
0
17) was achieved within 15 minutes, when 16 was stirred with indicated that approx. 28% conversion to tert-butyl acetate had
.1 eq of dried NaI in dry MeOH at 17 C. When common MeOH occurred.
ꢀ
(not dried) was used as the solvent, the quantitative esterica-
Another possibility for prepairing esters by the method
tion was observed aer 1 h with stirring at room temperature. reported here is to add carbonitriles to alcohols in the presence
We noticed that if more NaI (0.2–2 eq) was used in the reaction, of water. As an example, octanol (14a) was reuxed overnight
this generally reduced the reaction time. The same reaction was with dried Dowex® in common (not dried) acetonitrile or pro-
also performed without NaI at room temperature, but in that pionitrile, octyl acetate (19a) and octyl propionate (19b) were
case approx. 20% of oleic acid methyl ester (17) was formed. In isolated with 40% and 41% yields, respectively (without any
comparison, the same reaction was performed using conc. kind of reaction optimizations).
H SO as catalyst but in this case although the conversion to 17
was excellent aer 2 h reaction time, the H NMR spectrum as a nucleophile and as an example, the novel compound, 3-
indicated the formation of approx. 10% of side products. In (formyloxy)-2-phenylpropanoic acid (25) was prepared from
The present tool also makes it possible to use a formyl group
2
4
1
ꢀ
addition, direct esterication with bulkier alcohols, such as tropic acid (24) by stirring it in dry DMF overnight at 115 C
isopropanol is possible with the tool reported here, since 12- using 1 eq of NaI. Product 25 was isolated with 56% yield.
hydroxy-dodecanoic acid isopropyl ester (18) was obtained in a
straightforward manner from 14b with 70% isolated yield by etherication of a primary hydroxyl group (–CH
reuxing 14b for 4 h in 2-propanol and using 0.2 eq of NaI as secondary groups of D(+)-glucose (26) in one-pot. Without the
catalyst. protection of secondary hydroxyl groups, product 27 was iso-
Last but not least, we describe an example of selective
2
OH) over the
Based on the above experience, the method was then also lated with a high 83% yield as a pair of isomers (ratio 1 : 2).
tested for preparing biodiesel (23). Nowadays biodiesel is Traditionally, the selective substitution of a primary OH group
commonly prepared from triglycerides derived from plant from carbohydrates requires several protection and depro-
matter, such as vegetable oils using transesterication reaction. tection steps, but by using our novel tool such protection is not
The problems in the production processes are related to needed. We have preliminary results for another kind of
19
saponication (RCO
2 2 2
H + NaOH / RCO Na + H O), which substituent attached selectively to the primary hydroxyl group of
complicates the product separation, and the presence of water sugar with the method described here, but this will be reported
19
(
RCO Me + H O / RCO H + MeOH) which lowers the yields. elsewhere in the future.
2 2 2
Here, biodiesel was prepared from fatty acid triglycerides (22)
on a 10 ml scale by using cooking oil samples collected from the essential criteria of green chemistry. However, the
restaurants by a local company. Most of the water was separated possible formation of I and HI must be considered when
In summary, we conclude that the reported tool satises
2
and the material was used without further treatments. Typically, planning reactions to be made with this tool. When NaI was
1
approx. 90% yields and >95% purity (see Table 1 and H NMR used as catalytic amounts in the reactions there was usually
spectrum of product 23 and starting material 22 in the ESI†) no problem, but when it was used as reagent the crude
were obtained with this newly developed method.
reactions usually were dark in color probably due to the
We have demonstrated here how oleic acid can be effec- formation of I2 and possibly HI, and they needed to be
tively esteried to its methyl ester under extremely mild neutralized by sodium thiosulfate [see as an example the
conditions and how a real cooking oil sample can be converted detailed procedure for the synthesis of 2-(2-iodo-ethoxy)-
into biodiesel. We therefore considered another possibility, ethanol (13b) in ESI page S5†].
does this method work in the reverse direction: can alcohol be
esteried to its corresponding ester in an excess of carboxylic
acid? This proved to be possible, and as an example, iso-
Proposed reaction mechanisms
pentanol (20) can be esteried to isopentyl acetate (21) in In general, the exact reaction mechanism is difficult to deter-
acetic acid (1.9 eq) without any solvent by stirring a mixture of mine, even for simple chemical reactions. Typically the mech-
+
isopentanol (20), acetic acid (1.9 eq) and dried Dowex® H
anism is based on several routes or their combinations, such as
ꢀ
form for 2 hours at 50 C using 0.1 eq of dried NaI as the bond enthalpy and polarization, resonance structures, sterical
catalyst. Complete (100%) conversion to isopentyl acetate (21) effects and/or the entropy of the reactions. In this reaction
1
was observed according to the H NMR spectrum, but because system, one of the key features is sterical requirements, since
of the high volatility of 21, the isolated yield was “only” approx. the chain ends are more reactive in preference to other more
+
6
4%. As a comparison, quantitative conversion has been hindered positions. Moreover, the H form solid material
reported for the preparation of isopentyl acetate (21) starting favours proton transfer reactions from the solids to reagents,
ꢀ
from acetic acid and isopentanol (20) at 50 C by using lipase since ionic sodium iodide is less soluble in alcohols and polar
as a catalyst. However, the reported method needs ionic liquid/ aprotic solvents than the corresponding acid, e.g. HI. Most of
2
0
solid phase system as a reaction medium and in general, the the reactions illustrated in Table 1 can be explained based on
methods reported in the literature for preparation of 21 the sterical requirements and in situ formed hydrogen iodide,
require either higher temperatures and/or some kind of which is highly effective protonation agent (the pKa value for HI
21
solvent systems. In addition, when tert-butanol, acetic acid is ca. ꢁ10) for the generation of leaving groups and the
+
(
approx. 8 eq), dried Dowex® H form and 0.6 eq of dried NaI counter anionic iodide which is a good nucleophile with this
ꢀ
1
were stirred for 30 minutes at 80 C; the H NMR spectrum solid system. Even the catalytic esterication between acids and
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alcohols can possibly be attributed to the formation of HI, since
Notes and references
the highly reactive RCOI intermediate is formed via a stable
+
RC^O carbocation from RCO H aer water cleavage.
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2
In the case of esterication of alcohols with carbonitriles
(
RCN), the reaction is initiated with proton transfer from the
+
solid material to a cyanide moiety and a reactive R C]NH
compound is obtained. This intermediate reacts readily with
the excess of alcohol and water (1 eq) to the enthalpy favoured
ester product. Actually, the formation of trans-1,2-diiodoethene
derivatives (as compound 11) and formylation of alcohols are
the only products that cannot be explained directly in terms of
the above discussed reaction mechanism. In the rst case, we
propose that I
bond and in the latter case, one possible explanation may be a
reactive ICHO formed from Me NCHO (dimethyl formamide)
2
molecules are the species reacting with the triple
7 Z. Li. Wei-Dong, D. Wei-Guo and Z. Cheng-Han, Org. Lett.,
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2
aer alcohol addition leading to end product 25.
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9
M. R. dos Santos, J. R. Diniz, A. M. Arouca, A. F. Gomes,
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Conclusions
We have presented and demostarated a novel green chemistry
synthetic tool with which to prepare acid catalysed addition and
substitution reactions under mild reaction conditions. In the
10 F.-L. Wu, B. P. Ross and R. P. McGeary, Eur. J. Org. Chem.,
010, 1989.
2
+
reported tool, the salt form iodide anion over dry H form solid
11 K. Ramalinga, P. Vijayalakshmi and T. N. B. Kaimal,
material acted either as a reagent or as a catalyst. The method
Tetrahedron Lett., 2002, 43, 879.
makes it possible to conduct straightforward synthesis of a wide 12 D. C. Boffito, V. Crocell, C. Pirola, B. Neppolian, G. Cerrato,
variety of compounds, like esters, tertiary iodides or ethers, 1,2-
M. Ashokkumar and C. L. Bianchi, J. Catal., 2013, 297, 17.
diiodoethene derivatives, iodoalkanols and sugar derivatives in 13 G. B. B. Varadwaj, S. Rana and K. Parida, Chem. Eng. J., 2013,
a one-pot procedure without any protection steps but still with
excellent conversions. The tool will be advance for everyone
needed synthesis in their work and is denitely an interesting
starting point for nding novel methods for the synthesis of
radioiodine-labelled compounds. Finally, most of the reactions
849, 215.
1
1
1
4 V. Brahmkhatri and A. Patel, Appl. Catal., A, 2011, 403, 161.
5 X. Li and W. Eli, J. Mol. Catal., 2008, 279, 159.
6 A. A. Singh, S. N. A. Zulkii, M. Meyns, P. Y. Hayes and J. J. De
Voss, Tetrahedron: Asymmetry, 2011, 22, 1709.
reported here were also performed using regenerated Dowex® 17 S. P. Morcillo, L. A. de Cienfuegos, A. J. Mota, J. Justicia and
+
H cation exchange resin and they worked as well or even better
R. Robles, J. Org. Chem., 2011, 76, 2277.
than reactions performed with the original Dowex®.
18 W.-B. Pan, F.-R. Chang, L.-M. Wei, M.-J. Wu and Y.-C. Wu,
Tetrahedron Lett., 2003, 44, 331.
Acknowledgements
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2
0 P. Lozano, J. M. Bernal and A. Navarro, Green Chem., 2012,
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This research has been supported by strategic funding from the
University of Eastern Finland and Finnish Academy. The
authors would like to thank Mrs Maritta Salminkoski for her
expert technical assistance and Dr Janne Mauritz Weisell for
performing the MS measurements. The authors would also like
to thank, Dr Ewen MacDonald (retired) for correcting the
language of this and many of other our papers.
1
2
1 http://www.columbia.edu/ꢂcrg2133/Files/CambridgeIA/
Chemistry/AcidityBasicitykPa.pdf, accessed June 23, 2014.
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