Journal of Cleaner Production 14 (2006) 536e538

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Note from the field

A cleaner production method for the synthesis of bronopol e Abactericide that is useful in leather making

Lakshmi Muthusubramanian a,*, Rajat B. Mitra b

a Central Leather Research Institute, Adyar, Chennai e 600 020, Indiab National Chemical Laboratory, Pune e 411 008, India

Received 10 October 2004; accepted 11 March 2005

Available online 30 August 2005

Abstract

In leather industry environmental concern has been growing since 1980s. Increasing levels of pollutant emissions have reachedsaturation point in spite of the conventional technology that highly industrial countries have adopted to keep them under control. This

has started a technology revolution in several industries. These critical levels of pollution may have been caused by high industrialdensity, by high population density or by the use of old polluting technology. This situation has boosted emerging green technologywhich has begun to take up a larger portion of research work in the supply and raw materials in industries. Together with consumers

growing awareness of the environment, this new technology has ended up affecting the consumer good industry. In leather industrydue to the sector’s bad public image regarding pollution more emphasis has been given to clean technologies and waste reduction. Atthis time nearly every part of the tanning process has several cleaner or environmentally friendlier alternatives. In leather industry to

prevent damage to the hide and skin, bactericide is added during soaking process to kill the growth ofmicroorganism. Bronopol is usedas a bactericide. The active ingredient of bronopol is 2-bromo-2-nitropropane-1,3-diol. Here we have reported simple and cleanertechnology of the bronopol by using nontoxic and non-hazardous raw materials and belongs to the modern concept ofenvironmentally friendly low waste or nonwaste technology. Bronopol was characterized by IR and Mass spectral data.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Bronopol; IR; Mass spectra; Cleaner production in leather making

1. Introduction

Manufacturing of eco-leather through cleaner pro-duction concept is receiving new recognition today. It hasbeen realised that the industrialization in all the countrieshad been at some cost to public health and environment.The leather industry as well as other potential polluter iscontinuing to improve its environmentally friendlyprocedures in proportion to the regulatory legislation [1,2].

The conversion of animal hides and skins into usefulartifacts may be man’s oldest technology. Untreated

* Corresponding author. Block II, House No.18, Scientist Apart-

ments, C.L.R.I. Colony, Adyar, Chennai e 600 020, India.

0959-6526/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jclepro.2005.03.020

skins have limited value, because when wet they aresusceptible to bacterial attack and so they putrefy, but ifthey are dried they become inflexible and useless forpurposes such as clothing. These effects are eliminatedby addition of bactericide to the solution used in thesoaking process in leather industry by which putresciblebiological materials are converted into a stable materialwhich is resistant to microbial activities and which hasenhanced resistance to wet and dry heat [3,4]. In leatherindustry bacteria readily proliferate during the typicalsoaking process if left unreacted. Tanners are rightfullyconcerned about the extent of biological activity in theirsoaking process and the impact they can have on thegrain integrity and strength of the resulting leather.To prevent hide and skin from the bacterial attack,bactericide is added.

537L. Muthusubramanian, R.B. Mitra / Journal of Cleaner Production 14 (2006) 536e538

The earliest form of preservation is drying. Microor-ganism cannot digest a completely dry hide or skin.They need water to grow and multiply and produceenzymes. Enzymes need a wet environment to act ascatalysts. Many bacteria that cannot tolerate dryconditions die while others go into a dormant stageuntil moisture is available again. This is one reason whyeven when after a hide is thoroughly dried out and isapparently stable, if it becomes wet, decay will begin toset in within a few hours. Salt curing acts to preservehides by a combination of removing water from the hideand lowering the water activity of remaining moisture.Salt packs are historically the first method for hidepreservation. In this process the first hide is placed ona bed of salt, is then covered with salt and the next hideis placed on top. This process is repeated until the stackis several feet high. It requires about a pound of salt perpound of hide to do a thorough job of curing. Theprocess is much slower and takes as much as 30 days tocomplete [5,6]. Immediately after removal from theanimal, the fresh hides are chilled. Then they aretrimmed, fleshed and placed in insulated bins with icein preparation for shipment. Shipping the hides inrefrigerated trucks permits delays in processing of up tothreeefive days and extends, considerably, the distancethe hides can be moved. The downside is the expense ofice, extra-handling and refrigeration. Drying, salt curingand preserving in a chilled atmosphere are essential forlong term preservation [7,8].

Bacteria cannot live in the presence of certainchemical treatments. There are two classes of chemicaltreatments for bacteria, bacteristats that limit thegrowth of organisms at whatever stage they are in andbactericides that kill the organisms outright. Both thesetypes of materials are, at best, useful for short termpreservation. Many of the bactericides used in the pastwere based on mercury compounds, mixture of sulfiteand acetic acid, while these materials are very effectiveand are detrimental to the environment, and no longerin use for this purpose. Bronopol, which is used as

a bactericide in the leather industry, has the activeingredient of 2-bromo-2-nitropropane-1,3-diol. Earlierworkers have synthesized it by reacting bromo-nitro-methyl-cyclohexanol with formaldehyde [7,8]. We havedeveloped a simple, cleaner technology by reactingnitroalkane with formaldehyde under alkaline condi-tions, which on subsequent bromination results in thesynthesis of bronopol.

The reaction is as shown in Scheme 1.

2. Experimental

Sodium hydroxide (4.00 g, 0.10 mol) was dissolved in125 ml of methanol. The solution was cooled at 0 �C.To this, nitromethane (6.50 g, 0.12 mol) and formalde-hyde (37%) (6.00 g, 0.20 mol) were gradually addedduring 30 min. The reaction mixture was stirred at 0 �Cfor 1 h. Crystals of sodium salt of 2-nitropropane-1,3-diol separate out. To this mixture, bromine (24.00 g,0.15 mol) was added gradually at 0 �C. Bromine wasadded until the pale yellow colour persists. During thereaction bromine was used in slight excess. Completionof the reaction was determined by thin layer chroma-tography on pre-coated plastic silicagel sheets. Excessmethanol was removed under reduced pressure to obtaina pale yellow solid, which was dissolved in ethyl-acetateto precipitate sodium bromide. Sodium bromide wasfiltered off and the organic layer was removed underreduced pressure to collect the off-white crystalline 2-bromo-2-nitropropane-1,3-diol. The yield of the productwas 52% (11.00 g, 0.06 mol).

3. Results and discussion

The melting point of the newly synthesized com-pound was determined in open capillary tube. IRspectrum was obtained on Nicolet 20 DXB F.T.spectrometer. Mass spectra were recorded on 5890

Scheme 1.

538 L. Muthusubramanian, R.B. Mitra / Journal of Cleaner Production 14 (2006) 536e538

series II gas chromatograph with 5971 as a massselective detector.

MP: 128e130 �CIR (KBr) (cm�1): 3620 (OH), 2900 (eCH2e), 1520(CeNO2), 1350, 740 (CeBr)MS m/e (MC): 200

The IR spectrum of bronopol showed the character-istic absorption bands at 3620 cm�1 for aliphatichydroxyl groups, 2900 cm�1 for methylene groups,1350, 740 cm�1 for asymmetrical and symmetricalstretching of nitro groups, 740 cm�1 for CeBr groups.Mass spectral data showed the MC peak at 200.

4. Conclusion

In the leather industry, the earliest form ofpreservation of hides was drying. The disadvantage ofdrying alone, is that although the skins are not subjectto bacterial attack, they will be subject to insectinfestation which can cause just as much damage. Saltcuring is a much slower process and takes as much as30 days. The high capital investment required topurchase hides takes a 30 day storage period beforethey can be shipped, very unattractive. The disadvan-tage of this process remains in its impact on theenvironment. When the fresh hides are chilled ininsulated bins along with ice for shipment, thedownside with this alternative is the expense of ice,extra-handling and refrigeration. The methods de-scribed in this paper result in long term preservation.Bactericides are at best useful for short term preserva-tion, which kills the organisms outright. In this context,Bronopol is used as a bactericide in leather industry. Itsactive ingredient is 2-bromo-2-nitropropane-1,3-diol.Earlier workers have reported synthesis pathways thatinclude reaction of bromo-nitro-methyl-cyclohexanol

with aliphatic aldehyde. In this procedure cyclohexanol,which is expensive and sodium ethoxide which isa hazardous compound, are used. The procedure whichwe have developed is simple and is a cleaner technol-ogy. Our new, better process includes reaction offormaldehyde with nitroalkane under alkaline condi-tions using sodium hydroxide, containing methanol,which on bromination, results in the synthesis ofbronopol. Since the sodium salt of 2-nitropropanediol,does not react with alkyl halides, the sodium must belinked with the nitro group and bromine reacts easily toproduce the bromide compound. Raw materials such assodium hydroxide are inexpensive and methanol isa readily available commercial solvent which isrelatively nontoxic and non-hazardous, while sodiumethoxide is hazardous and expensive.

Work is now in progress with a commercial pro-duction facility to scale up the production of bronopol,using the process described in this paper.

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