ISSN 1023-1935, Russian Journal of Electrochemistry, 2007, Vol. 43, No. 11, pp. 1223–1228. © Pleiades Publishing, Ltd. 2007.Original Russian Text © Yu.G. Budnikova, T.V. Gryaznova, S.A. Krasnov, I.M. Magdeev, O.G. Sinyashin, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 11, pp. 1291–1296.

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INTRODUCTION

Development of science intensive, resource-saving,and environmentally clean technologies aimed atexport of high-technology products is currently one ofthe major strategies in science and technology. Electro-chemical technologies provide mild conditions ofchemical transformations and minimum use of toxicand fire-hazardous reagents, and lead to minimumwaste in production processes. Since oxidation andreduction are conducted without chemical reagents,processes may be environmentally clean (“green chem-istry”). These aspects have attracted considerable inter-est all over the world. Achievements in reactor engi-neering permit the scaling of the most promising reac-tions for industrial applications.

This review considers some of the recent achieve-ments and directions of research under innovation-ori-ented programs at the Arbuzov Institute of Organic andPhysical Chemistry.

The approaches to synthesis of useful productsdeveloped at the Institute are based on electrochemicalgeneration of catalysts and reagents. The latter include,for example, halogens, which are capable of acting(under certain conditions) as highly efficient halogenat-ing agents for

α

-olefins or rapeseed oil, leading to halo-paraffins having controllable halogen contents and use-ful as secondary plasticizers and other agents. This is a

radically new approach that satisfies the rigid ecologi-cal requirements to modern chemistry.

Electrochemical Halogenation of Unsaturated Compounds in Products of Petrochemical Synthesis

and Rapeseed Oil

Modern chemical industry has increasing demand inproducts with long-chain hydrocarbon radicals (

ë

16

andhigher) with various useful properties. Due to the pres-ence of a hydrophobic hydrocarbon fragment, paraffinswith substituted functional groups (

ë

16

–ë

28

) are usedfor the production of plasticizers; plastic lubricants;paintwork materials; pigments with improved wetting,dispersion, and modified viscosity; latex and resins;additives to diesel fuels, etc. However, there is no effec-tive technology for the preparation of these productsfrom inexpensive raw materials, for example, from pet-rochemical waste—higher

α

-olefins

ë

16

–ë

18

—or fromtheir accessible natural analog rapeseed oil, mainly con-sisting from higher unsaturated compounds (

ë

18

–ë

21

).

Today, design of an effective procedure for haloge-nation (primarily, chlorination) of higher industrial

α

-olefins obtained from

ë

16–18

, ë

20–26

, ë

28

, and higherfractions of hydrocarbon raw materials is of criticalimportance to Russia. These products are unreactive intraditional double-bond functionalization reactions. Toobtain higher chloroparaffins, industry generallyemploys classical chlorination of paraffins with ele-mentary chlorine. The use of gaseous chlorine is a dis-advantage of this procedure because this is a toxic, cor-rosive substance, hazardous in storage and handling.

Design of Ecologically Safe and Science Intensive Electrochemical Processes

1

Yu. G. Budnikova

z

, T. V. Gryaznova, S. A. Krasnov, I. M. Magdeev, and O. G. Sinyashin

Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Kazan, Russia

Received December 29, 2006

Abstract—

This review discusses the results of and prospects for studies aimed at design of new science inten-sive, environmentally safe technologies for the synthesis of organophosphorus compounds by halogenation of

α

-olefins, including modification of rapeseed oil; it also considers methods for the production of some otherintermediates for chemical industry. New synthetic applications have been developed, using combined methodsof classical organic chemistry and electrochemistry, for processes based on electrochemical generation of cat-alysts (mediators)—complexes of metals in low oxidation states, halogen complexes, etc. Selective electro-chemical procedures are suggested for the synthesis of triphenylphosphine, trialkylphosphates, and nanosizedtransition metal phosphides from white phosphorus.

Key words:

electrosynthesis, chemical technology, olefins, chloroparaffins, white phosphorus, metal phos-phides

DOI:

10.1134/S1023193507110018

1

This paper is taken from the Proceedings of the 16th All-RussianConference on Organic Electrochemistry, Novocherkassk,EKhOS-2006.

z

Corresponding author, e-mail: yulia@iopc.knc.ru

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BUDNIKOVA et al.

The available methods for electrochemical chlorinationof olefins also have serious drawbacks: the use of a dia-phragm type electrolyzer; impossibility of chlorinationof higher

α

-olefins under conditions that allow for gas-eous starting compounds and products; and applicabil-ity to chlorination alone, but not to bromination.

We have developed an effective, low-waste, ecolog-ically safe electrochemical procedure for the produc-tion of chloroparaffins—an alternative of the industrialprocedure using gaseous chlorine. Our method yields[1] chloroparaffins with controllable contents of chlo-rine (up to 50%) under mild conditions.

Electrolysis was conducted without separating theanode and cathode spaces, which facilitates technicalimplementation of the process. Reduction of the hydro-gen ions occurs on the cathode and liberates gaseoushydrogen; on the anode, highly active chlorine is gen-erated, which reacts with the olefin in the activelystirred electrolyte to form the corresponding chloroderivatives:

cathode process:

2

H

+

+ 2

e

H

2

,anode process: Cl

–

–

e

[Cl activ.],in electrolyte: [Cl activ.] + R

–

CH

=

CH

2

R

'

Cl

n

.These electrosyntheses showed that electrochemical

generation of the chlorinating agent in the presence ofhigher

α

-olefins leads to exhaustive (~100%) chlorina-tion into chloroparaffins (Table 1). Thus the

ë

16

–ë

18

and

ë

20–26

fractions are chlorinated at room tempera-ture; in the case of

ë

28

, chlorination takes place at themelting point of this fraction (

t

= 70°ë

). The scheme ofthe process may be represented by the following:

Scheme 1.

Charge

Starting reagents

CirculationEmulsion

Organic part(olefins)

Aqueous part(ël–)Product

Electrolysis actually takes place for the oil–watertwo-phase system, through which current is passedwhile vigorously stirring the mixture. After the processhas completed, the system segregates once again, andthe paraffin part is decanted. Since this approach leadsto a high degree of olefin chlorination, one can assumethat the product is formed by the radical mechanism,when the chlorine radicals generated on the anodereplace the hydrogen atoms of the hydrocarbon chain.The composition of the electrolyte was optimized [1]by varying the conditions of electrosynthesis for mostcomplete chlorination of olefins at minimal cost.

To obtain haloparaffins, electrolysis of the emul-sion of higher

α

-olefins of the

ë

16

–

ë

28

fractions andaqueous hydrohalogenic acid and its salt (molar ratioacid : salt : olefin = (2–14.2) : (0–3.5) : 1) was conductedin a diaphragmless electrolyzer at

20–90°C

. Hydrochlo-ric or hydrobromic acids were used for the hydrohalo-genic acid, and their sodium or potassium salts, for itssalt. Graphite, platinum, titanium, or glassy carbonwere employed for the cathode; graphite, platinum,ORTA, or glassy carbon, for the anode.

This procedure offers the advantage of selectiveradical halogenation of

α

-olefins, providing a control-lable content of chlorine (halogen) in the target pro-ducts and conducted under conditions of diaphragmlesselectrolysis. Haloparaffins are obtained with high pro-duct yields and current efficiency. Other advantages areas follows: no element halogens, generally used inindustrial processes; products with different halogencontents; use of

α

-olefins with different numbers ofcarbon atoms; mild conditions of halogenation, facili-tating the procedure; low voltage on the cell; low con-sumption of electric energy; simple design of electro-lyzer; easy separation of the product by decanting thehydrocarbon fraction that is insoluble in aqueous elec-trolyte.

Two continuous-operation diaphragmless electro-lyzers have been created as pilot samples with a currentload of up to 50 A. The process may be conducted at

20–90°ë

; anode current density is 100–1400 A/m

2

inaqueous hydrohalogenic acid or corresponding salt.Electrochemical chlorination of the

ë

16–18

fraction of

α

-olefins has been scaled, and pilot batches of chloro-paraffins with 25% and 49–50% chlorine have beensynthesized. The preliminary results of trials with twochloroparaffin samples used as secondary plasticizersin the production of polyvinylchloride film at theKaustik OAO (Sterlitamak) indicated that these prod-ucts comply with technical specifications for KhP-250and KhP-470 secondary industrial plasticizers (Table 2).

Rapeseed oil, which consists of 90% unsaturatedand polyunsaturated acids, is a promising substance forcreating various materials by modification of olefinsusing known reactions of unsaturated compounds. Theaim of these transformations is synthesis of productswith given properties from recyclable raw materials.Based on our experience in electrochemical chlorina-

Table 1.

Characteristics of chloroparaffins for differentamounts of electricity passed through the solution

Quantity of electricity,

F

[Cl], %

1 1.457 13.13 1.477 33.04 1.486 42.64.5 1.492 48.7

10 1.494 50.5

nD20

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DESIGN OF ECOLOGICALLY SAFE 1225

tion of higher olefins we have investigated the possibil-ity of synthesizing chlorinated products from rapeseedoil. It has been found that under the conditions stated in[1], one can obtain up to 25.8% chlorine in modifiedrapeseed oil. This corresponds to the addition of twochlorine atoms at each of the double bonds of the unsat-urated acid residue that is part of triglyceride. Furtherchlorination does not occur probably because of theincreased viscosity of the reaction mixture, which nowresembles light yellow paste, and also because of emul-sion decomposition. The viscosity of this chlorinatedrapeseed oil is almost independent of temperature,which may be useful for creating lubricants on its basis.Weak temperature dependence of viscosity is charac-teristic of cross-linked polymers. Therefore one canassume that radical chlorination is accompanied bypolymerization and cross-linking of the unsaturatedcompounds of rapeseed oil.

The mass spectrum of the product is complex fordefinite reasons, but the presence of the signals of

å

+

(

m

/

z

)

in the range 1735–2032 confirms that the com-pound has polymer components.

Electrosynthesis of Organophosphorus Compounds from White Phosphorus

With stringent economic and environmental regula-tions, manufacturers of organophosphorus compounds(OPCs) have recognized that direct functionalization ofwhite phosphorus is one of the major challenges in thisfield. Theoretical and experimental studies are neededto work out alternative direct routes to OPCs avoidingthe stage of chlorination and using elementary phos-phorus. The existing energy intensive industrial proce-dure for the synthesis of OPCs has become outdatedbecause it uses direct oxidation of white phosphoruswith chlorine with further phosphorylation of organicsubstrates with phosphorus chloride. The ensuing con-tamination of the atmosphere and sewage with chlorineand hydrogen chloride release creates serious problemsfor the environment. The growing commercial interestand stringent ecological requirements make researchersseek new, ecologically safe direct routes from whitephosphorus to various organophosphorus compounds.

Advances in the development of the scientific prin-ciples of electrochemical methods for the preparationof organophosphorus compounds from white phospho-rus are described in the literature [2–6]. Here we con-sider the procedures that are most promising from theviewpoint of applications, namely, electrosynthesis oftrialkylphosphates and triphenylphosphine, which arelarge-scale (semi-industrial) processes.

Synthesis of organic phosphines, phosphine oxides,and phosphoric acid ethers as unique ligands for cata-lysts, extractants for rare and transuranium elements,and flame retardants is of special interest in organo-phosphorus chemistry. Trialkyl and triaryl phosphateshave found use as plasticizers, additives to lubricants

and liquid fuels, extractants, complex-forming agents,herbicides, insecticides, and additives to polymers tomake the latter fire-proof substances capable of beingcolored with dyes; they are also employed as synthonsfor the preparation of other compounds with usefulproperties.

There is no one-stage industrial procedure for theproduction of phosphorus acid ethers or tertiary phos-phines from elementary phosphorus. The industrialmethod for the preparation of triphenylphosphine isbased on the interaction of a metallic sodium melt witharyl halide and phosphorus trihalide. Long time andhigh temperature of the process, as well as low purity ofthe product, are disadvantages of this technique. Trio-ctyl phospate is also produced according to the chlorinetechnology, under rigid conditions dictated by the diffi-culty of creating three bonds at phosphorus with bulkyoctyl substituents. There is no process for the produc-tion of these important compounds in Russia.

The aim of our recent studies has been the design ofa new simple, one-stage universal procedure for thesynthesis of OPCs directly from white phosphorus,with good yields and low waste, under environmentallyclean conditions avoiding traditional chlorinationstages. This a radically new approach to this problem.Based on the results of our studies we have attemptedto create an effective, ecologically acceptable processfor the electrosynthesis of these products.

We have suggested an effective method for selectiveelectrosynthesis of compounds with phosphorus–oxy-gen, phosphorus–nitrogen, and phosphorus–carbonbonds from white phosphorus under mild conditions[2–8]. Novel procedures have been created for the prep-aration of triphenylphosphine [8] and trialkyl phos-phate [7] directly from white phosphorus with 85–90%yields. Electrolysis of a mixture of white phosphorus,iodobenzene, and zinc bromide yields triphenylphos-phine; alcohol, iodide, or hydrochloric acid areincluded in the mixture for the synthesis of trialkylphosphate. An electrolyzer is a static cell without a dia-phragm, operating in a periodic mode.

Table 2.

Comparison of the quality indices of chlorinatedparaffins (from

α

-olefins C

16

–C

18

)

Chlorinated paraffin Density at 20

°

C, kg/m

3

Mass fraction of chlorine, %

Iodine number

Khimprom OAO

KhP-250 950–1020 24–29 –

KhP-470 1180 45–49 4

Electrochemical method

addition chlorination 950 24–26 2

substitution chlorination 1135 45–50 1

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BUDNIKOVA et al.

To achieve active reaction of white phosphorus itwas suggested that processes in the undivided cellshould be used simultaneously: formation of nucleo-philes (alkoxide, hydroxide, phenoxide, amide, andother ions) on the cathode and oxidation of halide ions(e.g., oxidation of the iodide ion to iodine) at the anode[2–6]. The diagram of the process presented belowshows that the reaction of P

4

with the products of elec-trode reactions leads to various phosphorus acid deriv-atives depending on the electrolysis conditions.

Scheme 2.

Electrolysis of dispersions of white phosphorus inalcohol solutions of tetraethylammonium iodideaffords a mixture of OPCs whose composition dependson the structure of the alcohol and reaction tempera-ture. Electrolysis in water–alcohol mixtures under opti-mal conditions with the stated ratio of reagents yieldstrialkyl phosphates with almost quantitative yields,including current efficiency [7]. In this case, the overallreaction is

The method suggested for the synthesis of trialkylphosphates is an almost wasteless procedure. It givesonly one by-product—hydrogen. In the systems understudy, the cathode-generated nucleophile acts as initia-tor of phosphorus rings cleavage, while the product ofiodide ion oxidation, promoting proton substitution inthe P–H bond, is regenerated in the course of electroly-sis and closes the cycle. Due to its high rate and selec-tivity, electrosynthesis leads to high conversion ofphosphorus into the target organophosphorus products[2–7].

Compounds with phosphorus–carbon bonds play animportant role in phosphorus chemistry. They havefound wide application as ligands in metallocomplexesthat show catalytic properties in industrial hydrogena-tion, hydroformylation, hydrosilylation, nitrogen fixa-tion, and other reactions; they are also useful as extrac-tants of heavy metal ions, for example, uranium and

+

-

cathodeP4

RO– (OH)

ROH(H2O)

–e

P(O)(OR3) (up 90%), R = Me, C6H13,PH(O)(OR2) (up 60%), R = Me, C4H9,[P(O)(OR)2]2O (up 80%), R = Pri, Bui, i-C5H11,H3PO3 (80%) etc.

I

anode

I2

P4 12ROH 4H2O 4 RO( )3PO 10H2.+ + +±20e

technetium ions, and also as complex-forming agentsand intermediates for the synthesis of other compoundswith valuable properties: phosphonium salts, phospho-ranes, etc.

We assumed that ê4 is capable of reacting with alkyland aryl halides under conditions of a metallocomplexcatalyst generated on an electrode [2–6]. Indeed, wehave succeeded in creating a new effective procedure ofselective electrosynthesis of compounds with P–Cbonds from white phosphorus in the presence of elec-trochemically generated catalysts—complexes of zero-valent nickel or zinc [8].

This process occurs with cathode reduction of theZn(II)L complex into a catalytically active formZn(0)L. Further reactions proceed in solution. ThusZn(0)L reacts with aryl halide to form the ArZnXL(complex by oxidative addition; the latter attacks thewhite phosphorus molecule with cleavage of P–P bondsand formation of P–C bonds, i.e., forming a three-coor-dinate phosphorus compound. Scheme 3 shows catalystregeneration and cycle closure [8]:

Scheme 3.

These investigations have laid the foundation fortechnological implementation of these processes andcreated the scientific basis for a highly effective,resource-saving, and ecologically safe procedure forelectrosynthesis of the most important classes of OPCs.These electrosynthesis procedures are patented.

The suggested routes to organophosphorus prod-ucts, which are steadily in demand, are radical innova-tions having a number of advantages. Electrochemicalgeneration of reagents capable of catalyzing phospho-rylation reactions of substrates with white phosphoruspermits one to avoid the difficulties and limitations oftraditional chemical procedures, demanding largeexcess of reagents for the reaction. Our approachallows control over the reaction rate and direction andultimately leads to the creation of new effective meth-ods for electrosynthesis of OPCs with P–C or P–Obonds.

Electrosynthesis of Metal Phosphidesfrom White Phosphorus

White phosphorus is reduced heterogeneously andoxidized at high potentials. However, the pronouncedactivity of P4with nucleophiles, leading to cleavage ofthe phosphorus–phosphorus bond, permits one to use itfor the synthesis (including electrochemical synthesis)

P4

anodecathode

–2e+2e

ArX

Zn0

Zn2+ PAr3

Zn2+

ArZnX

RUSSIAN JOURNAL OF ELECTROCHEMISTRY Vol. 43 No. 11 2007

DESIGN OF ECOLOGICALLY SAFE 1227

of phosphorus products with phosphorus–carbon,phosphorus–nitrogen, phosphorus–oxygen, and phos-phorus–metal bonds [2–8]. Electrochemical generationof various nucleophiles offers a unique opportunity forreactivity studies of phosphorus under conditions of insitu generation, aimed at synthesis of products undermild conditions. Of special interest in this respect aremetal phosphides, and especially those with usefulproperties such as conductivity, catalytic activity, etc.The reagents chosen for reactions with white phospho-rus included metal complexes and salts that are capableof being reduced to complexes of metals in the zero-valent state: Ni0, Co0, In0, Pd0, Rh0. Electrode reactionsproceed with consumption of a few electrons per metal-containing substrate molecule:

Mn+L + ne M0L, L = bipy, phen, solvent

M0L + P4 product [M–P]

and form products with phosphorus–metal bonds. Toverify these assumptions we have carried out prepara-tive electrolyses of mixtures of white phosphorus andmetal salt (complex) in diethylformamide in an electro-lyzer with separated anode and cathode spaces [9].

For reduction of white phosphorus in the coordina-tion sphere of the metallocomplex (metal in a lowdegree of oxidation) we chose compounds (Table 3)capable of being reduced at different cathode poten-tials. It was found that white phosphorus may be con-verted into metal phosphides under mild conditionsat room temperature (Table 3). In most cases, the2,2'-bipyridyl (bipy) or diphenylphosphinopyridine(Ph2Ppy) ligands, generally widely employed for stabi-lizing the reduced metal form in solution, were addedto the mixture. The metals not stabilized with the ligandoften deposit on the cathode. Phosphides with an organicfragment: Pd3P2bipy, Ni3P2bipy [9], Ni3P2(DMF) [9],Co3P2bipy, Co3P2(Ph2Ppy), RhP(DMF), and Zr3P2bipywere synthesized with high yields based on white phos-phorus (75–80%). Low yield (10%) was obtained in thecase of indium phosphide. This failure is probably asso-ciated with a very high reduction potential of the start-ing salt In2(SO4)3 and its poor solubility even in thepresence of a ligand.

Since the suggested procedure for the synthesis ofnickel phosphides is of great practical value, it seemedappropriate to obtain some additional informationabout the catalytic properties of these compounds,namely, to evaluate the surface area.

Ultrafine materials have recently attracted consider-able interest due to their unique isotropic structural andchemical properties. It was reported [10] that ultrafinematerials may possess unusual physical, mechanical,and chemical properties; in particular, they showunusual behavior in catalyzed and magnetic recordingprocesses [11–13]. Ultrafine amorphous alloys may beobtained by chemical and physical methods. The chem-ical procedures are based on chemical reduction andformation of a colloid gel solution; the physical meth-

ods use vapor deposition [14], etc. Increased interest inthe use of ultrafine amorphous metal alloys is dictatedby the necessity to increase the surface area and disper-sity of metal compounds [10].

The surface area of ultrafine amorphous materialsobtained by traditional methods, for example, by vapordeposition, is too small (0.1–0.01 m2/g) for these mate-rials to be used in industrial catalysis because of theirlow efficiency per mass unit of the catalyst. Ultrafineamorphous alloys obtained by chemical reduction havea large surface, 30–130 m2/g, and are much more effi-cient. We have found that the phosphide Ni3P2bipyobtained from white phosphorus and Ni(0)bipy gener-ated electrochemically has a very large surface area,200 m2/g; i.e., this is ultrafine material [9]. Thus thesuggested synthetic procedure affords ultrafine materi-als that can hardly be obtained by traditional methodsand hence may be used for creating new catalysts ontheir basis.

This work was supported by the Russian Founda-tion for Basic Research, grant nos. 04-03-32830,05-03-08039, 06-03-08019, 07-03-00213, INTAS,Complex OKhNM program nos. 1 and 8, ScientificSchool grant nos. NSh 5148.2006.3.

REFERENCES1. Budnikova, Yu.G., Magdeev, I.M., Reznik, V.S., Sin-

yashin, O.G., Tazeev, I.M., Yakushev, I.A. and Yarul-lin, R.S., RF Patent 228908, 2006.

2. Budnikova, Yu.G., Tazeev, D.I., Gryaznova, T.V., andSinyashin, O.G., Elektrokhimiya, 2006, vol. 42, p. 1252[Russ. J. Electrochem. (Engl. Transl.), vol. 42,pp. 1127–1133].

3. Budnikova, Yu.G., Ross. Khim. Zh., 2005, vol. 49, p. 81.4. Milyukov, V.A., Budnikova, Yu.G., and Sinyashin, O.G.,

Usp. Khim., 2005, vol. 74, p. 859.

Table 3. Electrochemical syntheses of metal phosphides inDMF

Starting metal salt (complex)

Reduction potential, V Product

NiBr2bipy –1.5 Ni3P2bipy

NiBr2phen –1.4 Ni3P2phen

NiBr2PPh3 –2.0 Ni3P2(DMF)

In2(SO4)3 + bipy –2.95 In3P2bipy

In2(SO4)3 –2.9 In3P2

PdCl2 + bipy –1.3 Pd3P2bipy

Co(BF4)2Ph2Ppy –1.95 Co3P2(Ph2Ppy)

Co(BF4)2bipy –1.70 Co3P2bipy

RhCl3 · 4H2O –1.45 Rh2P

Zr(SO4)2 · 4H2O + 2 bipy –2.1 Zr3P2bipy

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BUDNIKOVA et al.

5. Kargin, Yu.M., Budnikova, Yu.G., Martynov, B.I., Tury-gin, V.V., and Tomilov, A.P., J. Electroanal. Chem.,2001, vol. 507, p. 157.

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10. Lee, Sh.-P. and Chen, Y.-W., Ind. Eng. Chem. Res., 2001,vol. 40, p. 1495.

11. Chernogorenko, V.B., Muchnik, S.V., Lynchak, K.A.,and Klimak, Z.A., Mater. Res. Bull., 1981, vol. 16, p. 1.

12. Arinsson, B., Landstrom, T., and Rundqvist, S., Borides,Silicides, and Phosphides, New York: Wiley, 1965.

13. von Schnering, H.G. and Honle, W., Encyclopedia ofInorganic Chemistry, Chichester, UK: Wiley, 1994,vol. 6, p. 3106.

14. Sergeev, G.B., Nanokhimiya (Nanochemistry), Moscow:Univ. Knizh. Dom, 2006, pp. 53-61.