Iodine-catalyzed tandem synthesis of terminal acetals
and glycol mono esters from olefins and biomass-derived glycols
M. Arun Kumar, P. Swamy, M. Naresh, M. Mahender Reddy and N. Narender*
e-mail:I&PC Division, CSIR-IICT, Hyderabad 500 007, India.
narendern33@yahoo.co.in; Tel.: +91 40 27191703; fax: +91 40 27160387/757

Abstract
A new metal-free protocol is described for the synthesis of terminal acetals by tandem oxidative rearrangement of olefinsusing oxone as an oxidant in the presence of iodine in ethylene glycol (a versatile chemical derived from biomass or fossilfuels) medium. Moreover, a one-pot procedure for the preparation of glycol mono esters from olefins is also presented for thefirst time using the same reagent system.

Keywords: acetals, esters, diols, biomass, rearrangement

1. Introduction
In the last decade, the research of renewable reactants
has become a key issue for a sustainable chemistry [1].
Approximately 75% of the biomass produced by nature
through the process of photosynthesis corresponds tocarbohydrates, but only between 3% and 4% of thesecompounds are used for food and non-food purposes [2].
Therefore, the use of carbohydrates as raw materials forthe production of basic chemicals is an area of increasing
interests [3]. In this sense, a variety of glycols (1,2ethanediol, 1,2-propanediol, 1,2-butanediol, or 2,3butanediol) can be obtained from carbohydrates [1] aswell as from glycerol [4] via bio- or chemocatalytic
reactions. Those glycols could be used as starting
reactants to obtain products with higher added value.
The aim of the present work is to obtain terminal
acetals and glycolmono esters starting from olefins andglycols derived from biomass, through a tandem
oxidative rearrangement process (Scheme 1). Protectionof a carbonyl function as its acetal is a widely usedsynthetic route for the manipulation of various
multifunctional organic molecules [5]. Acetals can also be
used for C–C bond formations [6], the synthesis of ethers[7] and esters [8]. Classical methods for the synthesis ofacetals involve the treatment of aldehydes or ketones
with an alcohol using either a protic or Lewis acid catalyst[5]. Unfortunately, these procedures have somedisadvantages such as the use of corrosive and costly
reagents or additives and high catalyst loading. The
palladium(II)-catalyzed oxidation (Wacker process) ofterminal olefins in water furnishes the methyl ketones [9]and a similar reaction in alcohol gives theircorresponding internal acetals [10]. Acetalization at theterminal carbon atom of a cheaper terminal olefin insteadof a costlier aldehyde as substrate is a challenging task.
Consequently some Pd catalyzed protocols have beendeveloped for this important functional grouptransformation [11].

I2(5 mol%)RHOOHOxone(0.75 equiv)

ROxone(1.5 equiv)

RScheme 1OOOOHO

2. Materials and Methods
All chemicals used were reagent grade and used asreceived without further purification. 1H NMR spectra
were recorded at 300, 400 and 500 MHz and 13C NMR
spectra 75 MHz in CDCl3 or DMSO-D6. The chemical
shifts (δ) are reported in ppm units relative to TMS as aninternal standard for 1H NMR and CDCl3 for 13C NMR
spectra. Column chromatography was carried out using
silica gel (100-200 mesh).
General procedure for the synthesis of acetals/glycol mono esters
Oxone (1.5 mmol for acetal/ 3 mmol for glycol monoester) was slowly added to a well stirred solution ofolefine (2 mmol) and I2 (0.1 mmol) in ethylene glycol (2ml), then the reaction mixture was stirred at room
temperature. After completion of the reaction (asindicated by TLC), the reaction mixture was quenchedwith aqueous sodium thiosulfate and extracted with DCM(3×20 ml). Finally, the combined organic layer waswashed with water, dried over anhydrous Na2SO4 and thesolvent was evaporated under reduced pressure. The
crude reaction mixture was further purified by column
chromatography using silica gel (100-200 mesh) afforded
the pure products.

3. Results and Discussion
A variety of reaction conditions were employed toachieve the optimal conditions. The results revealed thata 2 : 1.5 : 0.1 mole ratio of styrene, oxone and I2 at room
temperature was shown to be the optimum reaction
conditions for terminal acetalization and 3 mmol of oxone
is required for complete conversion of olefin to ester.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

Table 1. Synthesis of acetals form various olefinsa
Entry

OlefinTime(h)ProductYieldb(%)

Table 2. Synthesis of esters from various olefinsa
Entry

OlefinYieldb
(%)

ProductO

1.3

1O

3.3

295

OO

O

1

OH

O

90

O

2OH

O

9490

O

33

O

3.3

4
O76

O

O

389

O

O

O

4O

55
Br

7PhPh

OHPhOH

PhO

Br95
6PhOH

PhPh

Ph

7PhPhPhO

OH

88648aOlefine (2 mmol), I2 (0.1 mmol), Oxone (1.5 mmol), Ethylene glycol (2ml), r.t. bProducts were characterized by NMR, mass spectra andquantified by GC.

After optimizing the reaction conditions, we exploredthe scope of this novel transformation with a variety ofolefins and yielded the corresponding acetals/esters ingood to excellent yields. Styrene produced the respective
terminal cyclic acetal/ester with excellent yield. Whereas,
relatively longer reaction times were required whereactivating or deactivating groups were present on thearomatic ring of styrene to provide excellent yields of thecorresponding acetals/esters. However, 2,4-dimethyl
styrene gave a relatively low yield, probably due to sterichindrance. Asymmetric and symmetric olefins also
underwent oxidative rearrangement and afforded goodyields of the corresponding acetals/esters. It is worth
mentioning that in the case of cyclic olefin, the ringcontraction product was observed.
Initial support for the proposed mechanism wasobtained by acetalization of styrene-β,β-d2, which gives abenzylic deuterated product. In situ ESI-MS and 13C
NMR experimental data also support the proposedmechanism. Further, computational studies at theB3LYP/6-31G* level, clearly demonstrate the propensity
for O- attack on α-C rather than on β-C in the phenonium
ion intermediate.

4. Conclusions
In conclusion, we have developed a remarkably mild,
efficient and selective metal-free method for thesynthesis of terminal acetals from olefins in biomassderived glycols. A one pot protocol for the preparation ofglycol mono esters from olefins has also been introduced
using the same reagent system.

OHO
O

OH

Ph80

O

1.3

8

BrO O

760

OO O

2.3OHO

O

51

95
5

6OOBrOHOO
OOHOO

OH

65-60

aOlefine (2 mmol), I2 (0.1 mmol), Oxone (3 mmol), Ethylene glycol (2ml), 24 h, r.t. bProducts were characterized by NMR, mass spectra andquantified by GC.

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7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013