global class CampaignReminder
{

  WebService static void SendReminder(string id)
    {
     
      id cmpid = id;
      Integer batchSize = 1; 
      database.executebatch(new SendeMailinBatch(cmpid) , batchSize);
       
    }
}
=================batch process====
global class SendeMailinBatch implements Database.Batchable<sObject>,Database.Stateful 
{ 
  Public id campaignid;
  global SendeMailinBatch(id campid) 
   { 
       campaignid = campid;
   }
  global Database.QueryLocator start(Database.BatchableContext BC) 
   { 
      //Batch on all campaign memeber who belongs to the requetsed campaign 
      String query = 'select id, emailtobesentid__c from campaignmember where campaignid = :campaignid'; 
      return Database.getQueryLocator(query); 
   }
  global void execute(Database.BatchableContext BC, List<sObject> scope) 
   { 
      //***  Select the campaign details
      List<campaignmember> cmx = new list<campaignmember>();
      campaign cmp = new campaign();
      cmp = [ select id, From_eMail__c, Reply_To__c, templatetobesent__c from campaign where id = :campaignid ];  
      for(Sobject s : scope) 
      { 
          //Type cast sObject in campaign object 
          campaignmember CM = (campaignmember)s ; 
          //Sending Mail
          Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
          mail.setSenderDisplayName(cmp.From_eMail__c);
          mail.setReplyTo(cmp.Reply_To__c);
          mail.setTargetObjectId(CM.emailtobesentid__c);
          mail.setTemplateId(cmp.templatetobesent__c);
          Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail});
      }
   }
   global void finish(Database.BatchableContext BC) 
   { 
     
   } 
}