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## MODES FOR CARRYING OUT THE INVENTION 

1brough intensive research, the inventors have discovered that by adding inorganic weak base solution, organic weak base solution or combination thereof into a water solution containing the compound of formula I or a mixture solution of water and organic solvent containing the compound of for› mula I, and adjusting pH value of the solution to 4.0-7 .0, a solution of micafungin sodium ofhigh purity can be prepared. The method is easily operated and ofhighreproducibility, and the quality of product is high, therefore, the method is well suited for industrial production. 

## Process of Invention and Analysis of the Principle 

Generally, there are two ways for preparing acid into sodium salt. One is exchange using cationic resin; the other is via adjusting pH value. Virtually, preparing sodium salt by adjusting pH value is a process of neutralization reaction between acid and base. It includes two types of reactions, i.e. the reaction between strong acid and strong base, and the reaction between strong acid and weak base. If strong base solution is added into strong acid solution for adjusting pH value, there is a sharp change in the pH value of the solution (the change of pH value is illustrated in FIG. 6), and the pH value will be instantly altered by 8. Therefore in the practical production, it is hard to control the pH value and a slightest mistake could lead to an overregulated pH value. In WO2004014879, a 0.1 mol/L NaOH solution was used to adjust pH value to 6-8 for obtaining formula II compound. It was actually a reaction between strong acid and strong base. The compound of formula I contains benzene sulfonic acid groups and pKa values of benzene sulfonic acid compounds are generally less than 1, therefore the compound is strong acid compound (See FIG. 1). Therefore, theoretically, the method using NaOH solution to adjust pH values for obtain› ing sodium salt is unsuitable for preparation of formula II compound. 

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The inventors have repeated the method reported in WO2004014879 for multiple times and analyzed and vali› dated the reported method from the point of view oflocal pH value. The inventors have found that during the course of pH adjusting, regarding the whole solution system, 0.1 mol/L NaOH solution has a relatively low concentration and the overall pH value can be managed at 6-8, however, during the course of adding NaOH solution dropwise, the local base concentration gets too high, i.e. local pH value in the solution gets overly high, therefore, partial degradation occurred in micafungin, hence the impurity content is much too high. See FIGS. 1, 2 and 3. FIG. 1 shows the HPLC purity of formula I compound before pH adjustment. FIGS. 2 and 3 show HPLC purities after formula I compound is adjusted in pH value with 0.1 mol/L NaOH solution, in which obvious degradation can be found. 

In order to avoid the aforesaid prominent defects, the inventors have conducted further and intensive researches and have unexpectedly found that by using inorganic weak base solution, organic weak base solution or combinations 

thereof to adjust pH value of solution of formula I compound, compound of formula II can be obtained without generating extra impurities. The inventors have conducted in-depth analysis on the cause of the sound result from the aforesaid weak base solution. First of all, there exists within the weak base solution an ionization equilibrium. The molecules are in a state of incomplete ionization and possess a certain degree of buffer capacity. Therefore, when adjusting the pH value, there is not an obvious pH surge, as is shown in FIG. 7. While using 0.1 M NaHCO$_{3 }$ solution to titrate the solution of micaf› ungin, the pH changes slowly and there is not an obvious pH surge, and the pH value can be stably remained at 7, thus facilitating the pH control during the practical production. Secondly, compared with the strong base solution, weak base solutions of the same concentration per se have lower pH values. During the course of adding the weak base solution into the solution of formula I compound, the local pH value won’t readily rise. Therefore, using weak base solution to adjust the pH of the solution of formula I compound for preparing sodium salt is a method much suited for the prepa› ration of formula II compound. In addition, the inventors, via further in-depth studies, further unexpectedly found that the concentration of weak base solution will also influence the sodium salt preparation via adjustment of pH. In theory, the lower the concentrations of weak bases, the better the results, however, overly low concentration obviously does not con- form to the practical requirements in the production. Based on the experiment data, the concentration of the weak base is preferably at 0.001-1 mol/L, for achieving the best effects. 

The inventors have also conducted further researches and discussions for determining the pKa values of the conjugate acid corresponding to the weak base. The test results showed that the pKa value of the conjugate acid corresponding to the weak base is preferably at 4-11, most preferably 5-8. ThepKa value is a particular balance constant which represents the capacity of an acid to dissociate hydrogen ion. The lower the pKa value, the strong its capacity to offer proton, hence a stronger acidity, a smaller alkalinity ofits corresponding con› jugate base has, and vice versa. The equation to calculate pKa is: pKa=-1 g[H+][A-]/[HA] (HA stands for weak acid, H+ is the hydrogen ion ionized from the weak acid HA, A- is an anion ionized from the weak acid HA). The compound of Formula I is a sulfonic acid compound of strong acid type. In a solution, it is almost completely ionized, and the pKa thereof is generally lower than 1. Therefore, it can facilitate the reaction to take place when encounter a weak base ( con› jugate acid pKa=4). When the compound of formula I reacts with the weak base and generates a weak acid with the pKa value of 4, via the aforesaid equation of pK, it can be calcu- lated that the concentration of weak acid [HA] generated in the solution is 100 times the concentration of [H+] or [A-]. Since the concentration of residue [H+] is comparable with that of the residue formula I compound, the concentration of generated weak acid [HA] is 100 times higher than that of the residue [formula I compound], that is, 99% of the formula I compound has been transformed into the form of sodium salt. When formula I compound reacted with the weak base and generates a weak acid with pKa of 11, it can be calculated via the aforesaid equation that the concentration of the weak acid [HA] generated in the solution is 3.16xl0 $^{5 }$times that of [H+] or [A-]. Likewise, 99 .99% of formula I compound has trans› formed into a sodium salt form. Lastly, based on the experi› ment results, it is verified that pKa value of the conjugate acid of the weak base should be chosen at 4-11, for achieving the optimum effects. 

The inventors have also discovered via experiments on stability of micafungin in solutions with different pH that 

