Patent Description:
Rare earth elements refer to <NUM> metal elements including <NUM> lanthanides having atomic numbers from <NUM> to <NUM> in the periodic table of elements, and scandium with atomic number of <NUM> and yttrium with atomic number of <NUM>, which have similar chemical properties with lanthanides. Rare earth elements have unique magnetic, optical and electrical properties, and are known as "industrial vitamins". They are widely used in metallurgical industry, petrochemical industry, glass ceramics, energy materials, military industry and other fields, and are important fundamental raw materials for the development of human society.

At present, mining of rare earth minerals in nature comprises steps of: leaching rare earth ions with leaching agent to obtain rare earth leachate, and then extracting and separating rare earth ions one by one through solvent extraction. The development of extractants is the core technology of solvent extraction process, and many factors have to be considered when selecting the extractants for rare earth metals used in industry, such as extraction selectivity, extraction rate, extraction capacity, stability of the compound, solubility, back extraction performance, safety, synthesis method and source, etc. An excellent extractant is one in a million, and a good extractant can simplify production process, improve separation efficiency, reduce production cost and reduce pollution discharge.

Commercially available extractant products known in the field mainly include organic phosphine extractants, carboxylic acid extractants and amine extractants. Typical organic phosphine extractants include phosphonic acid mono(<NUM>-ethylhexyl)ester (P507), di(<NUM>-ethylhexyl) phosphonic acid (P204), di(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid (C272) and tributyl phosphonate(TBP)and the like, the amine extractants include tri-n-octylamine (N235), secondary carbon primary amine (N1923), methyl trioctyl ammonium chloride (N263), and the like, and the carboxylic acid extractants include naphthenic acid, neodecanoic acid, secondary octyl phenoxyacetic acid (CA-<NUM>) and the like.

Commercially available extractants still have some shortcomings. For example, P507 is the most widely used extractant in rare earth separation industry, but its separation coefficient for adjacent rare earth elements is low. For example, the separation coefficient for praseodymium and neodymium is only <NUM>, which makes it difficult to separate praseodymium and neodymium elements. Naphthenic acid is mainly used to separate and purify yttrium oxide. However, naphthenic acid is a by-product of petrochemical industry, and its composition is complex, so rare earth elements can be extracted under higher pH conditions. After long-term use, its composition is easy to change, which leads to the decrease of organic phase concentration and affects the stability of separation process. CA-<NUM> extractant has been tried to replace naphthenic acid, which can effectively separate yttrium from all lanthanides in the extraction and separation process of rare earth elements and can overcome the problem that the concentration of organic phase decreases when yttrium is extracted and separated by naphthenic acid. However, the separation coefficient for heavy rare earth elements and yttrium in the extraction system is low, which makes it difficult to separate heavy rare earth elements from yttrium, so it is necessary to design more stages of extraction tanks to achieve the separation effect.

Amide carboxylic acid is a new type of extractant containing N and O ligands, and has certain selectivity for the extraction of transition metal ions, stable chemical structure and fast extraction kinetics, thus it is a promising extractant.

The prior art discloses preparation methods of various amide carboxylic acid compounds, for example, <CIT> discloses a new method for synthesizing N,N,N',N'-tetraoctyl-<NUM>-oxopentanediamide (TODGA) comprising the following steps: (<NUM>) diglycolic acid reacts with SOCl<NUM> to obtain diglycolyl chloride which then reacts with amine to obtain partial TODGA; (<NUM>) water-soluble components are removed from the byproduct, and then monooxamidecarboxylic acid is obtained by separating the product; and (<NUM>) the monooxamidecarboxylic acid reacts with amine to further obtain part of TODGA. This process combines the characteristics of existing processes and has a high yield.

<CIT> provides a synthesis method of imide modified low molecular weight line type phenolic resin, which comprises the following steps: in N,N-dimethylformamide or a mixed solvent mainly containing N,N-dimethylformamide, para-aminophenol reacts with anhydride of dicarboxylic acid to obtain an amide carboxylic acid phenolic compound, and then the amide carboxylic acid phenolic compound and <NUM>,<NUM>-dimethylol p-cresol undergo polycondensation reaction and dehydration ring closure reaction under the catalysis of acidic catalysts, such as oxalic acid, etc, so as to obtain the imide modified low molecular weight line type phenolic resin.

<CIT> discloses a bis-diglycidyl amide ligand, a preparation method thereof and a separation and extraction system for lanthanides/actinides containing the bis-diglycidyl amide ligand, wherein the separation and extraction system is formed by mixing an organic phase and aqueous phase in equal volume, and the organic phase contains N,N,N',N',N",N"-hexa-n-octyl nitrilotriacetamide with a molar concentration of <NUM>-<NUM> mol/L as extractant. N,N,N',N',N",N"-hexa-n-octyl nitrilotriacetamide in the extraction system of this invention has a unique non-N heterocyclic triangular structure, which not only can greatly improve the radiation-resistant of the extraction system, but also does not produce secondary pollutants, which is favorable for the environment. The water-soluble bis-diglycidyl amide ligand is used as masking agent in the extraction system, which is more inclined to complex with the lanthanides, and can effectively mask the lanthanides in the aqueous phase, thus realizing the selective separation of actinides and lanthanides.

<CIT> discloses an extraction agent for europium or light rare earths, comprising an amide derivative represented by the following formula, wherein, R<NUM> and R<NUM> each represent the same or different alkyl groups; the alkyl group is optionally a straight chain or a branched chain; R<NUM> represents a hydrogen atom or an alkyl group; and R<NUM> represents a hydrogen atom or any group other than an amino group, which is bound to the α carbon as an amino acid.

From the above, it can be seen that although the prior art provides preparation methods of amide carboxylic acid, it does not provide amide carboxylic acid compounds which can more effectively separate rare earth elements and an extraction separation method thereof. In order to separate rare earth elements more effectively, it is necessary to develop a new extractant having higher separation coefficient compared with the prior art and can overcome the shortcomings in the prior art, and an extraction separation method using thereof.

To overcome the shortcomings of the prior art, an object of the present invention is to provide an N,N-dihydrocarbyl amide carboxylic acid, a preparation method therefor and use thereof. N,N-dihydrocarbyl amide carboxylic acid can be used as an extractant for separating and purifying selected rare earth elements from a mixed rare earth feed liquid, especially for extracting and separating yttrium element from mixed rare earth elements.

In order to achieve the above object, the present invention adopts the following technical solution:
In a first aspect, the present invention provides an N,N-dihydrocarbyl amide carboxylic acid with a structure represented by the following Formula I:
<CHM>.

The present invention provides an amide carboxylic acid compound with a structure represented by Formula I as a carboxylic acid extractant for separating rare earth elements and an extraction separation method using the same. This kind of compound has not been reported as extractant for rare earth elements. As a metal extractant, this kind of compound has high separation coefficient for rare earth elements, especially for separating heavy rare earth elements and yttrium element, and can overcome the shortcomings of naphthenic acid in separating yttrium.

Preferably, the hydrocarbyl is any one selected from the group consisting of substituted alkyl, substituted alkenyl and substituted alkynyl, wherein the substituents of the substituted alkyl, the substituted alkenyl and the substituted alkynyl are each independently any one or a combination of at least two selected from the group consisting of halogen, hydroxyl, carboxyl, acyl, ester group, ether group, alkoxy, phenyl, phenoxy, amino, amido, nitro, cyano, mercapto, sulfonyl, thiol, imino, sulfonyl and sulfanyl. Preferably, the substituents are halogens.

Preferably, R<NUM> and R<NUM> are each independently a linear or branched, saturated or unsaturated, and substituted or unsubstituted C6-C30 hydrocarbyl; preferably a linear or branched, saturated or unsaturated, and substituted or unsubstituted C6-C18 hydrocarbyl.

Preferably, R<NUM> and R<NUM> are each independently a linear or branched, saturated or unsaturated, and substituted or unsubstituted C6 or more hydrocarbyl, such as linear or branched, and unsubstituted (C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C22, C24, C26, C28, C30, C35, C40, etc.) alkyl, alkenyl, alkynyl; preferably a branched, saturated or unsaturated, and unsubstituted C6-C30 hydrocarbyl; more preferably a branched, saturated or unsaturated, and unsubstituted C6-C10 hydrocarbyl.

Preferably, R<NUM> and R<NUM> are each independently a linear or branched, and unsubstituted C6-C30 alkyl; preferably a linear or branched, and unsubstituted C6-C18 alkyl; and more preferably a linear or branched, and unsubstituted C6-C10 alkyl.

Preferably, n is a natural number from <NUM> to <NUM>.

Preferably, R<NUM> and R<NUM> are each independently
<CHM>
wherein, <NUM>≤a+b≤<NUM>,
<CHM>
represents connecting site.

Preferably, R<NUM> and R<NUM> are independently any one of the following groups, wherein,
<CHM>
represent connecting site,
<CHM>
<CHM>
<CHM>
<CHM>.

Preferably, R<NUM> is selected from a linear or branched, saturated or unsaturated, and substituted or unsubstituted C6 or more (such as, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C30, C40, etc.) hydrocarbyl; preferably a linear or branched, saturated or unsaturated, and substituted or unsubstituted C6-C30 hydrocarbyl.

Preferably, R<NUM> is selected from a linear or branched, unsaturated and unsubstituted C6 or more (such as, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, etc.) hydrocarbyl; preferably a linear C10 or more alkenyl; and more preferably linear C10-C18 alkenyl.

Preferably, R<NUM> is any one selected from the group consisting of the following groups, wherein,
<CHM>
represent connecting site,
<CHM>
<CHM>
<CHM>.

In a second aspect, the present invention provides a method for preparing N,N-dihydrocarbyl amide carboxylic acid according to the first aspect, comprising a step of:.

Preferably, the molar ratio of N,N-dihydrocarbyl secondary amine represented by Formula II to anhydride compound represented by Formula III is <NUM> : (<NUM>-<NUM>). For example, it may be <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, etc..

Preferably, the molar ratio of N,N-dihydrocarbyl secondary amine represented by Formula II to carboxylic acid monoacyl chloride represented by Formula IV is <NUM> : (<NUM>-<NUM>). For example, it may be <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, <NUM> : <NUM>, etc..

Preferably, the temperature for mixing and reacting N,N-dihydrocarbyl secondary amine represented by Formula II and anhydride compound represented by Formula III is <NUM> to <NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. The mixing and reacting time is <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc..

Preferably, the temperature of for mixing and reacting N,N-dihydrocarbyl secondary amine represented by Formula II and carboxylic acid monoacyl chloride represented by Formula IV is <NUM> to <NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc. The mixing and reacting time is <NUM>-<NUM>, for example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc..

Preferably, N,N-dihydrocarbyl secondary amine represented by Formula II and anhydride compound represented by Formula III are mixed and reacted in the absence of a solvent; or in an inert solvent.

Preferably, N,N-dihydrocarbyl secondary amine represented by Formula II and carboxylic acid monoacyl chloride represented by Formula IV are mixed and reacted in the absence of a solvent; or in an inert solvent.

In the present invention, it is worth mentioning that the reaction can also be carried out in the absence of a solvent, and the compound with the structure represented by Formula II and the compound with the structure represented by Formula III are directly mixed and reacted.

Preferably, the inert solvent is selected from any one or a combination of at least two selected from the group consisting of hexane, dichloromethane, petroleum ether, toluene, xylene or kerosene.

In a third aspect, the present invention provides use of the N,N-dihydrocarbyl amide carboxylic acid according to the first aspect in preparing an extractant for separating rare earth elements.

Preferably, the separating rare earth elements specifically refers to extracting and separating yttrium element from a mixture of rare earth elements.

Compared with the prior art, the present invention has the following advantageous effects.

In the following, the technical solution of the present invention will be further explained with reference to the drawings and specific embodiments. It should be understood to those skilled in the art that the detailed description is intended to aid in the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

The present Example provides a compound I-<NUM> represented by Formula I, which has a structural formula as follows:
<CHM>.

Compound I-<NUM> was prepared by the synthesis route as follows:
<CHM>.

The synthesis method can be carried out with or without a solvent, and the synthesis method with a solvent was as follows:.

The synthesis method without a solvent was as follows:
N,N-dihydrocarbyl secondary amine represented by Formula II-<NUM> (<NUM>, <NUM> mol) and anhydride compound represented by Formula III-<NUM> (<NUM>, <NUM> mol) were directly mixed to form a mixed solution, and the mixed solution was stirred while heating to <NUM> and then kept at <NUM> for two hours. After the reaction was finished, the compound I-<NUM> was obtained.

Or N,N-dihydrocarbyl secondary amine represented by Formula II-<NUM> and carboxylic acid-monoacyl chloride compound represented by Formula III-1a were mixed and reacted, as shown in the following Reaction Scheme:
<CHM>.

The synthesis method was as follows: N,N-dihydrocarbyl secondary amine represented by Formula II-<NUM> (<NUM>, <NUM> mol) and carboxylic acid-monochloride compound represented by Formula III-1a (<NUM>, <NUM> mol) were directly mixed to form a mixed solution, and the mixed solution was stirred while heating to <NUM> and then kept at <NUM> for two hours. After the reaction was finished, compound I-<NUM> was obtained.

In the present invention, the compound I-<NUM> was analyzed by nuclear magnetic resonance, and the results were shown in <FIG>.

The analysis of NMR Hydrogen spectrum (<FIG>) was as follows: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM> (<NUM>), <NUM> (<NUM>), <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

Among them, peaks at <NUM>~<NUM> were assigned to hydrogen of alkyl chain in compound I-<NUM>; peak at <NUM> was assigned to hydrogen of methylene in
<CHM>
structure; peak at <NUM> was assigned to hydrogen of methylidyne in
<CHM>
structure and hydrogen of methylene in
<CHM>
structure; peaks at <NUM> and <NUM> were assigned to two hydrogens of olefin in
<CHM>
structure; and peak at <NUM> was assigned to hydrogen of carboxyl.

The analysis of carbon-<NUM> nuclear magnetic resonance spectrum (<FIG>) was as follows: <NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

Among them, peaks at <NUM>~<NUM> were assigned to carbon of alkyl chain in compound I-<NUM>; peaks at <NUM> and <NUM> were assigned to carbon of methylidyne in the
<CHM>
structure; peak at <NUM> was assigned to carbon of methylene in
<CHM>
structure; peak at172. <NUM> was assigned to carbon of amide carbonyl and peak at <NUM> was assigned to carbon of carboxyl.

The present Example provides a compound I-<NUM> represented by Formula I, which has a structural Formula as follows:
<CHM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR(<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM> (<NUM>), <NUM> (<NUM>), <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR(<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(4C), <NUM>, <NUM>, <NUM>(4C).

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM> (<NUM>), <NUM> (<NUM>), <NUM>(<NUM>), <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>(2C), <NUM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR(<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR(<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR(<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>.

<NUM>C NMR(<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

NMR characterization of compound I-<NUM>: <NUM>H NMR(<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR(<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(8C), <NUM>(16C), <NUM>, <NUM>(4C), <NUM>, <NUM>, <NUM>(6C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>(52C), <NUM>, <NUM>, <NUM>(2C), <NUM>.

NMR characterization of compound I-<NUM>: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(36C), <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C).

NMR characterization of compound I-<NUM>:.

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C).

Comparative Example <NUM> provides a compound I-d1 represented by Formula I-d1, which has a structural Formula as follows:
<CHM>.

Compound I-d1 was prepared by the synthesis route as follows:
<CHM>.

NMR characterization of compound I-d1: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>(2C).

Comparative Example <NUM> provides a compound I-d2 represented by Formula I-d2, which has a structural Formula as follows:
<CHM>.

Compound I-d2 was prepared by the synthesis route as follows:
<CHM>.

NMR characterization of compound I-d2: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>.

Comparative Example <NUM> provides a compound I-d3 represented by Formula I-d3, which has a structural Formula as follows:
<CHM>.

Compound I-d3 was prepared by the synthesis route as follows:
<CHM>.

NMR characterization of compound I-d3: <NUM>H NMR (<NUM>, CDCl<NUM>), δ <NUM> (<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>), <NUM>(<NUM>).

<NUM>C NMR (<NUM>, CDCl<NUM>), δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>(2C), <NUM>, <NUM>, <NUM>(2C).

The specific test results (total enrichment ratio of rare earth ions) were shown in Table <NUM>.

It can be seen from the above table that the enrichment ratio of N,N-dihydrocarbyl amide carboxylic acid prepared according to in Examples <NUM> to <NUM> is above <NUM>%, while the total enrichment ratio of N,N-dihydrocarbyl amide carboxylic acid in Comparative Examples <NUM> to <NUM> is below <NUM>%. Therefore, the N,N-dihydrocarbyl amide carboxylic acid according to the present invention can be used as extractant to enrich rare earth elements from raw material containing low-concentration rare earth elements with better enrichment effect.

The specific test results (relative separation coefficient βLn/Y of rare earth ions (Ln) relative to yttrium ions (Y)) were shown in Table <NUM>.

It can be seen from table <NUM> that the separation coefficient (βLn/Y) of N,N-dihydrocarbyl amide carboxylic acids of Examples <NUM> to <NUM> for each rare earth element is higher than that of Comparative Examples <NUM> to <NUM>. The N,N-dihydrocarbyl amide carboxylic acids defined by the present invention can better separate and purify yttrium element from mixed rare earth raw materials.

The stability of compound I-<NUM> prepared in the above Example <NUM> was tested by the following procedure: compound I-<NUM> was prepared into an extractant solution by dissolving <NUM> of compound I-<NUM> in <NUM> of toluene to prepare an extractant solution with a concentration of <NUM> mol/L; <NUM> of extractant solution and <NUM> of hydrochloric acid solution with concentration of <NUM> mol/L were mixed and stirred for <NUM> days, and another <NUM> of extractant solution and <NUM> of sodium hydroxide solution with concentration of <NUM> mol/L were mixed and stirred for <NUM> days, and then the extractant loss rate in both was tested by NMR. The stability of compounds according to Examples <NUM> to <NUM> and Comparative Examples was tested in the same manner as that of compound I-<NUM>.

Specific test results (the extractant loss rate in hydrochloric acid medium and liquid caustic soda medium) were shown in Table <NUM> below.

It can be seen from the test data in table <NUM> that the loss rate of N,N-dihydrocarbyl amide carboxylic acid in hydrochloric acid medium was below <NUM>%; and the loss rate in liquid caustic soda medium was below <NUM>%. Therefore, it is fully proved that the N,N-dihydrocarbyl amide carboxylic acids prepared by the present invention have excellent chemical stability and can withstand strong acid and strong alkali without decomposition.

Claim 1:
An N,N-dihydrocarbyl amide carboxylic acid with a structure represented by Formula I:
<CHM>
wherein, R<NUM> and R<NUM> are each independently a linear or branched, saturated or unsaturated, and unsubstituted C6 or more hydrocarbyl;
R<NUM> is a linear or branched, saturated or unsaturated, and unsubstituted C6 or more hydrocarbyl; and
n is a natural number from <NUM> to <NUM>.